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• gluCylinder() how works OpenGL

  - by amin__

  I wanted to build a cricket ground with OpenGL. I made several polygons to indicate field, pitch and bowling lines. But the problem is when I am trying to use gluCylinder to make stumps I made depth glEnable(GL_DEPTH_TEST), but my polygons are then not working. I just want to know how Can I use gluCylinder to make stumps with those polygons I have made. I have following code, but want to add stumps here but I cant, #include <GL/gl.h> #include <GL/glut.h> static double deg=0.0; void display(void) { glClear (GL_COLOR_BUFFER_BIT); glRotatef(deg, 0.0, 0.0, 1.0); // Rotate by deg // field glColor3f (0.0, 0.5, 0.0); glBegin(GL_POLYGON); glVertex3f (0, 0, 0.0); glVertex3f (1, 0, 0.0); glVertex3f (1, 0.75, 0.0); glVertex3f (0.8, 0.82, 0.0); glVertex3f (0.6, 0.85, 0.0); glVertex3f (0.4, 0.85, 0.0); glVertex3f (0.2, 0.82, 0.0); glVertex3f (0.0, 0.75, 0.0); glEnd(); // pitch glColor3f (0.25, 0.30, 0.0); glBegin(GL_POLYGON); glVertex3f(0.5,0.65,0.0); glVertex3f(0.47,0.35,0.0); glVertex3f(0.60,0.35,0.0); glVertex3f(0.57,0.65,0.0); glEnd(); //ump line glColor3f (1.0, 1.0, 1.0); glBegin(GL_POLYGON); glVertex3f(0.49,0.63,0.0); glVertex3f(0.49,0.6315,0.0); glVertex3f(0.58,0.6315,0.0); glVertex3f(0.58,0.63,0.0); glEnd(); //bat line glColor3f (1.0, 1.0, 1.0); glBegin(GL_POLYGON); glVertex3f(0.46,0.40,0.0); glVertex3f(0.46,0.4025,0.0); glVertex3f(0.61,0.4025,0.0); glVertex3f(0.61,0.40,0.0); glEnd(); glFlush (); } void init (void) { glClearColor (0.0, 0.0, 0.0, 0.0); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0); } void keyboard(unsigned char key, int x, int y) { switch (key) { case 27: // "esc" on keyboard exit(0); break; case 97: // "a" on keyboard deg = deg+5.0; glutPostRedisplay(); break; case 100: deg = deg-5.0; glutPostRedisplay(); break; } } int main(int argc, char** argv) { glutInit(&argc, argv); glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); glutInitWindowSize (600, 600); glutInitWindowPosition (100, 100); glutCreateWindow ("hello"); init (); glutDisplayFunc(display); glutKeyboardFunc(keyboard); glutMainLoop(); return 0; }

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• mysql_close doesn't kill locked sql requests

  - by Nikita

  I use mysqld Ver 5.1.37-2-log for debian-linux-gnu I perform mysql calls from c++ code with functions mysql_query. The problem occurs when mysql_query execute procedure, procedure locked on locked table, so mysql_query hangs. If send kill signal to application then we can see lock until table is locked. Create the following SQL table and procedure CREATE TABLE IF NOT EXISTS `tabletolock` ( `id` INT NOT NULL AUTO_INCREMENT, PRIMARY KEY (`id`) )ENGINE = InnoDB; DELIMITER $$ DROP PROCEDURE IF EXISTS `LOCK_PROCEDURE` $$ CREATE PROCEDURE `LOCK_PROCEDURE`() BEGIN SELECT id INTO @id FROM tabletolock; END $$ DELOMITER; There are sql commands to reproduce the problem: 1. in one terminal execute lock tables tabletolock write; 2. in another terminal execute call LOCK_PROCEDURE(); 3. In first terminal exeute show processlist and see | 2492 | root | localhost | syn_db | Query | 12 | Locked | SELECT id INTO @id FROM tabletolock | Then perfrom Ctrl-C in second terminal to interrupt our procudere and see processlist again. It is not changed, we already see locked select request and can teminate it by unlock tables or kill commands. Problem described is occured with mysql command line client. Also such problem exists when we use functions mysql_query and mysql_close. Example of c code: #include <iostream> #include <mysql/mysql.h> #include <mysql/errmsg.h> #include <signal.h> // g++ -Wall -g -fPIC -lmysqlclient dbtest.cpp using namespace std; MYSQL * connection = NULL; void closeconnection() { if(connection != NULL) { cout << "close connection !\n"; mysql_close(connection); mysql_thread_end(); delete connection; mysql_library_end(); } } void sigkill(int s) { closeconnection(); signal(SIGINT, NULL); raise(s); } int main(int argc, char ** argv) { signal(SIGINT, sigkill); connection = new MYSQL; mysql_init(connection); mysql_options(connection, MYSQL_READ_DEFAULT_GROUP, "nnfc"); if (!mysql_real_connect(connection, "127.0.0.1", "user", "password", "db", 3306, NULL, CLIENT_MULTI_RESULTS)) { delete connection; cout << "cannot connect\n"; return -1; } cout << "before procedure call\n"; mysql_query(connection, "CALL LOCK_PROCEDURE();"); cout << "after procedure call\n"; closeconnection(); return 0; } Compile it, and perform the folloing actions: 1. in first terminal local tables tabletolock write; 2. run program ./a.out 3. interrupt program Ctrl-C. on the screen we see that closeconnection function is called, so connection is closed. 4. in first terminal execute show processlist and see that procedure was not intrrupted. My question is how to terminate such locked calls from c code? Thank you in advance!

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• Data Warehouse ETL slow - change primary key in dimension?

  - by Jubbles

  I have a working MySQL data warehouse that is organized as a star schema and I am using Talend Open Studio for Data Integration 5.1 to create the ETL process. I would like this process to run once per day. I have estimated that one of the dimension tables (dimUser) will have approximately 2 million records and 23 columns. I created a small test ETL process in Talend that worked, but given the amount of data that may need to be updated daily, the current performance will not cut it. It takes the ETL process four minutes to UPDATE or INSERT 100 records to dimUser. If I assumed a linear relationship between the count of records and the amount of time to UPDATE or INSERT, then there is no way the ETL can finish in 3-4 hours (my hope), let alone one day. Since I'm unfamiliar with Java, I wrote the ETL as a Python script and ran into the same problem. Although, I did discover that if I did only INSERT, the process went much faster. I am pretty sure that the bottleneck is caused by the UPDATE statements. The primary key in dimUser is an auto-increment integer. My friend suggested that I scrap this primary key and replace it with a multi-field primary key (in my case, 2-3 fields). Before I rip the test data out of my warehouse and change the schema, can anyone provide suggestions or guidelines related to the design of the data warehouse the ETL process how realistic it is to have an ETL process INSERT or UPDATE a few million records each day will my friend's suggestion significantly help If you need any further information, just let me know and I'll post it. UPDATE - additional information: mysql> describe dimUser; Field Type Null Key Default Extra user_key int(10) unsigned NO PRI NULL auto_increment id_A int(10) unsigned NO NULL id_B int(10) unsigned NO NULL field_4 tinyint(4) unsigned NO 0 field_5 varchar(50) YES NULL city varchar(50) YES NULL state varchar(2) YES NULL country varchar(50) YES NULL zip_code varchar(10) NO 99999 field_10 tinyint(1) NO 0 field_11 tinyint(1) NO 0 field_12 tinyint(1) NO 0 field_13 tinyint(1) NO 1 field_14 tinyint(1) NO 0 field_15 tinyint(1) NO 0 field_16 tinyint(1) NO 0 field_17 tinyint(1) NO 1 field_18 tinyint(1) NO 0 field_19 tinyint(1) NO 0 field_20 tinyint(1) NO 0 create_date datetime NO 2012-01-01 00:00:00 last_update datetime NO 2012-01-01 00:00:00 run_id int(10) unsigned NO 999 I used a surrogate key because I had read that it was good practice. Since, from a business perspective, I want to keep aware of potential fraudulent activity (say for 200 days a user is associated with state X and then the next day they are associated with state Y - they could have moved or their account could have been compromised), so that is why geographic data is kept. The field id_B may have a few distinct values of id_A associated with it, but I am interested in knowing distinct (id_A, id_B) tuples. In the context of this information, my friend suggested that something like (id_A, id_B, zip_code) be the primary key. For the large majority of daily ETL processes (80%), I only expect the following fields to be updated for existing records: field_10 - field_14, last_update, and run_id (this field is a foreign key to my etlLog table and is used for ETL auditing purposes).

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• [C#][XNA] Draw() 20,000 32 by 32 Textures or 1 Large Texture 20,000 Times

  - by Rudi

  The title may be confusing - sorry about that, it's a poor summary. Here's my dilemma. I'm programming in C# using the .NET Framework 4, and aiming to make a tile-based game with XNA. I have one large texture (256 pixels by 4096 pixels). Remember this is a tile-based game, so this texture is so massive only because it contains many tiles, which are each 32 pixels by 32 pixels. I think the experts will definitely know what a tile-based game is like. The orientation is orthogonal (like a chess board), not isometric. In the Game.Draw() method, I have two choices, one of which will be incredibly more efficient than the other. Choice/Method #1: Semi-Pseudocode: public void Draw() { // map tiles are drawn left-to-right, top-to-bottom for (int x = 0; x < mapWidth; x++) { for (int y = 0; y < mapHeight; y++) { SpriteBatch.Draw( MyLargeTexture, // One large 256 x 4096 texture new Rectangle(x, y, 32, 32), // Destination rectangle - ignore this, its ok new Rectangle(x, y, 32, 32), // Notice the source rectangle 'cuts out' 32 by 32 squares from the texture corresponding to the loop Color.White); // No tint - ignore this, its ok } } } Caption: So, effectively, the first method is referencing one large texture many many times, each time using a small rectangle of this large texture to draw the appropriate tile image. Choice/Method #2: Semi-Pseudocode: public void Draw() { // map tiles are drawn left-to-right, top-to-bottom for (int x = 0; x < mapWidth; x++) { for (int y = 0; y < mapHeight; y++) { Texture2D tileTexture = map.GetTileTexture(x, y); // Getting a small 32 by 32 texture (different each iteration of the loop) SpriteBatch.Draw( tileTexture, new Rectangle(x, y, 32, 32), // Destination rectangle - ignore this, its ok new Rectangle(0, 0, tileTexture.Width, tileTexture.Height), // Notice the source rectangle uses the entire texture, because the entire texture IS 32 by 32 Color.White); // No tint - ignore this, its ok } } } Caption: So, effectively, the second method is drawing many small textures many times. The Question: Which method and why? Personally, I would think it would be incredibly more efficient to use the first method. If you think about what that means for the tile array in a map (think of a large map with 2000 by 2000 tiles, let's say), each Tile object would only have to contain 2 integers, for the X and Y positions of the source rectangle in the one large texture - 8 bytes. If you use method #2, however, each Tile object in the tile array of the map would have to store a 32by32 Texture - an image - which has to allocate memory for the R G B A pixels 32 by 32 times - is that 4096 bytes per tile then? So, which method and why? First priority is speed, then memory-load, then efficiency or whatever you experts believe.

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• MVC: returning multiple results on stream connection to implement HTML5 SSE

  - by eddo

  I am trying to set up a lightweight HTML5 Server-Sent Event implementation on my MVC 4 Web, without using one of the libraries available to implement sockets and similars. The lightweight approach I am trying is: Client side: EventSource (or jquery.eventsource for IE) Server side: long polling with AsynchController (sorry for dropping here the raw test code but just to give an idea) public class HTML5testAsyncController : AsyncController { private static int curIdx = 0; private static BlockingCollection<string> _data = new BlockingCollection<string>(); static HTML5testAsyncController() { addItems(10); } //adds some test messages static void addItems(int howMany) { _data.Add("started"); for (int i = 0; i < howMany; i++) { _data.Add("HTML5 item" + (curIdx++).ToString()); } _data.Add("ended"); } // here comes the async action, 'Simple' public void SimpleAsync() { AsyncManager.OutstandingOperations.Increment(); Task.Factory.StartNew(() => { var result = string.Empty; var sb = new StringBuilder(); string serializedObject = null; //wait up to 40 secs that a message arrives if (_data.TryTake(out result, TimeSpan.FromMilliseconds(40000))) { JavaScriptSerializer ser = new JavaScriptSerializer(); serializedObject = ser.Serialize(new { item = result, message = "MSG content" }); sb.AppendFormat("data: {0}\n\n", serializedObject); } AsyncManager.Parameters["serializedObject"] = serializedObject; AsyncManager.OutstandingOperations.Decrement(); }); } // callback which returns the results on the stream public ActionResult SimpleCompleted(string serializedObject) { ServerSentEventResult sar = new ServerSentEventResult(); sar.Content = () => { return serializedObject; }; return sar; } //pushes the data on the stream in a format conforming HTML5 SSE public class ServerSentEventResult : ActionResult { public ServerSentEventResult() { } public delegate string GetContent(); public GetContent Content { get; set; } public int Version { get; set; } public override void ExecuteResult(ControllerContext context) { if (context == null) { throw new ArgumentNullException("context"); } if (this.Content != null) { HttpResponseBase response = context.HttpContext.Response; // this is the content type required by chrome 6 for server sent events response.ContentType = "text/event-stream"; response.BufferOutput = false; // this is important because chrome fails with a "failed to load resource" error if the server attempts to put the char set after the content type response.Charset = null; string[] newStrings = context.HttpContext.Request.Headers.GetValues("Last-Event-ID"); if (newStrings == null || newStrings[0] != this.Version.ToString()) { string value = this.Content(); response.Write(string.Format("data:{0}\n\n", value)); //response.Write(string.Format("id:{0}\n", this.Version)); } else { response.Write(""); } } } } } The problem is on the server side as there is still a big gap between the expected result and what's actually going on. Expected result: EventSource opens a stream connection to the server, the server keeps it open for a safe time (say, 2 minutes) so that I am protected from thread leaking from dead clients, as new message events are received by the server (and enqueued to a thread safe collection such as BlockingCollection) they are pushed in the open stream to the client: message 1 received at T+0ms, pushed to the client at T+x message 2 received at T+200ms, pushed to the client at T+x+200ms Actual behaviour: EventSource opens a stream connection to the server, the server keeps it open until a message event arrives (thanks to long polling) once a message is received, MVC pushes the message and closes the connection. EventSource has to reopen the connection and this happens after a couple of seconds. message 1 received at T+0ms, pushed to the client at T+x message 2 received at T+200ms, pushed to the client at T+x+3200ms This is not OK as it defeats the purpose of using SSE as the clients start again reconnecting as in normal polling and message delivery gets delayed. Now, the question: is there a native way to keep the connection open after sending the first message and sending further messages on the same connection?

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• Replace conditional with polymorphism refactoring or similar?

  - by Anders Svensson

  Hi, I have tried to ask a variant of this question before. I got some helpful answers, but still nothing that felt quite right to me. It seems to me this shouldn't really be that hard a nut to crack, but I'm not able to find an elegant simple solution. (Here's my previous post, but please try to look at the problem stated here as procedural code first so as not to be influenced by the earlier explanation which seemed to lead to very complicated solutions: http://stackoverflow.com/questions/2772858/design-pattern-for-cost-calculator-app ) Basically, the problem is to create a calculator for hours needed for projects that can contain a number of services. In this case "writing" and "analysis". The hours are calculated differently for the different services: writing is calculated by multiplying a "per product" hour rate with the number of products, and the more products are included in the project, the lower the hour rate is, but the total number of hours is accumulated progressively (i.e. for a medium-sized project you take both the small range pricing and then add the medium range pricing up to the number of actual products). Whereas for analysis it's much simpler, it is just a bulk rate for each size range. How would you be able to refactor this into an elegant and preferably simple object-oriented version (please note that I would never write it like this in a purely procedural manner, this is just to show the problem in another way succinctly). I have been thinking in terms of factory, strategy and decorator patterns, but can't get any to work well. (I read Head First Design Patterns a while back, and both the decorator and factory patterns described have some similarities to this problem, but I have trouble seeing them as good solutions as stated there. The decorator example seems very complicated for just adding condiments, but maybe it could work better here, I don't know. And the factory pattern example with the pizza factory...well it just seems to create such a ridiculous explosion of classes, at least in their example. I have found good use for factory patterns before, but I can't see how I could use it here without getting a really complicated set of classes) The main goal would be to only have to change in one place (loose coupling etc) if I were to add a new parameter (say another size, like XSMALL, and/or another service, like "Administration"). Here's the procedural code example: public class Conditional { private int _numberOfManuals; private string _serviceType; private const int SMALL = 2; private const int MEDIUM = 8; public int GetHours() { if (_numberOfManuals <= SMALL) { if (_serviceType == "writing") return 30 * _numberOfManuals; if (_serviceType == "analysis") return 10; } else if (_numberOfManuals <= MEDIUM) { if (_serviceType == "writing") return (SMALL * 30) + (20 * _numberOfManuals - SMALL); if (_serviceType == "analysis") return 20; } else //i.e. LARGE { if (_serviceType == "writing") return (SMALL * 30) + (20 * (MEDIUM - SMALL)) + (10 * _numberOfManuals - MEDIUM); if (_serviceType == "analysis") return 30; } return 0; //Just a default fallback for this contrived example } } All replies are appreciated! I hope someone has a really elegant solution to this problem that I actually thought from the beginning would be really simple... Regards, Anders

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• Having trouble storing a CRTP based class in a vector

  - by user366834

  Hi, Im not sure if this can be done, im just delving into templates so perhaps my understanding is a bit wrong. I have a Platoon of soldiers, the platoon inherits from a formation to pick up the formations properties, but because i could have as many formations as i can think of I chose to use the CRTP to create the formations, hoping that i could make a vector or array of Platoon to store the platoons in. but, of course, when i make a Platoon, it wont store it in the vector, "types are unrelated" Is there any way around this ? i read about "Veneers" which are similar and that they work with arrays but i cant get it to work, perhaps im missing something. here's some code: (sorry about the formatting, the code is here in my post but its not showing up for some reason ) template < class TBase > class IFormation { public : ~IFormation(){} bool IsFull() { return m_uiMaxMembers == m_uiCurrentMemCount; } protected: unsigned int m_uiCurrentMemCount; unsigned int m_uiMaxMembers; IFormation( unsigned int _uiMaxMembers ): m_uiMaxMembers( _uiMaxMembers ), m_uiCurrentMemCount( 0 ){} // only allow use as a base class. void SetupFormation( std::vector<MySoldier*>& _soldierList ){}; // must be implemented in derived class }; ///////////////////////////////////////////////////////////////////////////////// // PHALANX FORMATION class Phalanx : public IFormation<Phalanx> { public: Phalanx( ): IFormation( 12 ), m_fDistance( 4.0f ) {} ~Phalanx(){} protected: float m_fDistance; // the distance between soldiers void SetupFormation( std::vector<MySoldier*>& _soldierList ); }; /////////////////////////////////////////////////////////////////////////////////// // COLUMN FORMATINO class Column : public IFormation< Column > { public : Column( int _numOfMembers ): IFormation( _numOfMembers ) {} ~Column(); protected: void SetupFormation( std::vector<MySoldier*>& _soldierList ); }; I then use these formations in the platoon class to derive, so that platoon gets the relevant SetupFormation() function: template < class Formation > class Platoon : public Formation { public: **** platoon code here }; everything works great and as expected up until this point. now, as my general can have multiple platoons, I need to store the platoons. typedef Platoon< IFormation<> > TPlatoon; // FAIL typedef std::vector<TPlatoon*> TPlatoons; TPlatoon m_pPlatoons m_pPlatoons.push_back( new Platoon<Phalanx> ); // FAIL, types unrelated. typedef Platoon< IFormation< TPlatoon; fails because i need to specify a template parameter, yet specifying this will only allow me to store platoons created with the same template parameter. so i then created FormationBase class FormationBase { public: virtual bool IsFull() = 0; virtual void SetupFormation( std::vector<MySoldier*>& _soldierList ) = 0; }; and made IFormation publicly inherit from that, and then changed the typedef to typedef Platoon< IFormation< FormationBase > > TPlatoon; but still no love. now in my searches i have not found info that says this is possible - or not possible.

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• Reordering Variadic Parameters

  - by void-pointer

  I have come across the need to reorder a variadic list of parameters that is supplied to the constructor of a struct. After being reordered based on their types, the parameters will be stored as a tuple. My question is how this can be done so that a modern C++ compiler (e.g. g++-4.7) will not generate unnecessary load or store instructions. That is, when the constructor is invoked with a list of parameters of variable size, it efficiently pushes each parameter into place based on an ordering over the parameters' types. Here is a concrete example. Assume that the base type of every parameter (without references, rvalue references, pointers, or qualifiers) is either char, int, or float. How can I make it so that all the parameters of base type char appear first, followed by all of those of base type int (which leaves the parameters of base type float last). The relative order in which the parameters were given should not be violated within sublists of homogeneous base type. Example: foo::foo() is called with arguments float a, char&& b, const float& c, int&& d, char e. The tuple tupe is std::tuple<char, char, int, float, float>, and it is constructed like so: tuple_type{std::move(b), e, std::move(d), a, c}. Consider the struct defined below, and assume that the metafunction deduce_reordered_tuple_type is already implemented. How would you write the constructor so that it works as intended? If you think that the code for deduce_reodered_tuple_type, would be useful to you, I can provide it; it's a little long. template <class... Args> struct foo { // Assume that the metafunction deduce_reordered_tuple_type is defined. typedef typename deduce_reordered_tuple_type<Args...>::type tuple_type; tuple_type t_; foo(Args&&... args) : t_{reorder_and_forward_parameters<Args>(args)...} {} }; Edit 1 The technique I describe above does have applications in mathematical frameworks that make heavy use of expression templates, variadic templates, and metaprogramming in order to perform aggressive inlining. Suppose that you wish to define an operator that takes the product of several expressions, each of which may be passed by reference, reference to const, or rvalue reference. (In my case, the expressions are conditional probability tables and the operation is the factor product, but something like matrix multiplication works suitably as well.) You need access to the data provided by each expression in order to evaluate the product. Consequently, you must move the expressions passed as rvalue references, copy the expressions passed by reference to const, and take the addresses of expressions passed by reference. Using the technique I describe above now poses several benefits. Other expressions can use uniform syntax to access data elements from this expression, since all of the heavy-lifting metaprogramming work is done beforehand, within the class. We can save stack space by grouping the pointers together and storing the larger expressions towards the end of the tuple. Implementing certain types of queries becomes much easier (e.g. check whether any of the pointers stored in the tuple aliases a given pointer). Thank you very much for your help!

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• Fill container with template parameters

  - by phlipsy

  I want to fill the template parameters passed to a variadic template into an array with fixed length. For that purpose I wrote the following helper function templates template<typename ForwardIterator, typename T> void fill(ForwardIterator i) { } template<typename ForwardIterator, typename T, T head, T... tail> void fill(ForwardIterator i) { *i = head; fill<ForwardIterator, T, tail...>(++i); } the following class template template<typename T, T... args> struct params_to_array; template<typename T, T last> struct params_to_array<T, last> { static const std::size_t SIZE = 1; typedef std::array<T, SIZE> array_type; static const array_type params; private: void init_params() { array_type result; fill<typename array_type::iterator, T, head, tail...>(result.begin()); return result; } }; template<typename T, T head, T... tail> struct params_to_array<T, head, tail...> { static const std::size_t SIZE = params_to_array<T, tail...>::SIZE + 1; typedef std::array<T, SIZE> array_type; static const array_type params; private: void init_params() { array_type result; fill<typename array_type::iterator, T, last>(result.begin()); return result; } }; and initialized the static constants via template<typename T, T last> const typename param_to_array<T, last>::array_type param_to_array<T, last>::params = param_to_array<T, last>::init_params(); and template<typename T, T head, T... tail> const typename param_to_array<T, head, tail...>::array_type param_to_array<T, head, tail...>::params = param_to_array<T, head, tail...>::init_params(); Now the array param_to_array<int, 1, 3, 4>::params is a std::array<int, 3> and contains the values 1, 3 and 4. I think there must be a simpler way to achieve this behavior. Any suggestions? Edit: As Noah Roberts suggested in his answer I modified my program like the following: I wrote a new struct counting the elements in a parameter list: template<typename T, T... args> struct count; template<typename T, T head, T... tail> struct count<T, head, tail...> { static const std::size_t value = count<T, tail...>::value + 1; }; template<typename T, T last> stuct count<T, last> { static const std::size_t value = 1; }; and wrote the following function template<typename T, T... args> std::array<T, count<T, args...>::value> params_to_array() { std::array<T, count<T, args...>::value> result; fill<typename std::array<T, count<T, args...>::value>::iterator, T, args...>(result.begin()); return result; } Now I get with params_to_array<int, 10, 20, 30>() a std::array<int, 3> with the content 10, 20 and 30. Any further suggestions?

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• Strange thing on IPv6 multicast program on Windows

  - by zhanglistar

  I have written an ipv6 multicast program on windows xp sp3. But a problem bothers me a lot. The sendto function implies no error, but I can't capture the packet using wireshark. I am sure the filter is right. Thanks in advance. And the code is as follows: #include "stdafx.h" #include <stdio.h> /* for printf() and fprintf() */ #include <winsock2.h> /* for socket(), connect(), sendto(), and recvfrom() */ #include <ws2tcpip.h> /* for ip_mreq */ #include <stdlib.h> /* for atoi() and exit() */ #include <string.h> /* for memset() */ #include <time.h> /* for timestamps */ #include <pcap.h> #include <Iphlpapi.h> #pragma comment(lib, "Ws2_32.lib") #pragma comment(lib, "wpcap.lib") #pragma comment(lib, "Iphlpapi.lib") int _tmain(int argc, _TCHAR* argv[]) { int sfd; int on, length, iResult; WSADATA wsaData; struct addrinfo Hints; struct addrinfo *multicastAddr, *localAddr; char buf[46]; // Initialize Winsock iResult = WSAStartup(MAKEWORD(2, 2), &wsaData); if (iResult != 0) { printf("WSAStartup failed: %d\n", iResult); return 1; } /* Resolve destination address for multicast datagrams */ memset(&Hints, 0, sizeof (Hints)); Hints.ai_family = AF_INET6; Hints.ai_socktype = SOCK_DGRAM; Hints.ai_protocol = IPPROTO_UDP; Hints.ai_flags = AI_NUMERICHOST; iResult = getaddrinfo("FF02::1:2", "547", &Hints, &multicastAddr); if (iResult != 0) { /* error handling */ printf("socket error: %d\n", WSAGetLastError()); return -1; } /* Get a local address with the same family (IPv4 or IPv6) as our multicast group */ Hints.ai_family = multicastAddr->ai_family; Hints.ai_socktype = SOCK_DGRAM; Hints.ai_flags = AI_PASSIVE; /* Return an address we can bind to */ if ( getaddrinfo(NULL, "546", &Hints, &localAddr) != 0 ) { printf("getaddrinfo() failed: %d\n", WSAGetLastError()); exit(-1); } // Create sending socket //sfd = socket (multicastAddr->ai_family, multicastAddr->ai_socktype, multicastAddr->ai_protocol); sfd = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP); if (sfd == -1) { printf("socket error: %d\n", WSAGetLastError()); return 0; } /* Bind to the multicast port */ if ( bind(sfd, localAddr->ai_addr, localAddr->ai_addrlen) != 0 ) { printf("bind() failed: %d\n", WSAGetLastError()); exit(-1); } if (multicastAddr->ai_family == AF_INET6 && multicastAddr->ai_addrlen == sizeof(struct sockaddr_in6)) /* IPv6 */ { on = 1; if (setsockopt (sfd, IPPROTO_IPV6, IPV6_MULTICAST_IF, (char *)&on, sizeof (on) /*(char *)&interface_addr, sizeof(interface_addr)*/) == -1) { printf("setsockopt error:%d\n", WSAGetLastError()); return -1; } if (setsockopt (sfd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, (char *)&on, sizeof (on) /*(char *)&interface_addr, sizeof(interface_addr)*/) == -1) { printf("setsockopt error:%d\n", WSAGetLastError()); return -1; } struct ipv6_mreq multicastRequest; /* Multicast address join structure */ /* Specify the multicast group */ memcpy(&multicastRequest.ipv6mr_multiaddr, &((struct sockaddr_in6*)(multicastAddr->ai_addr))->sin6_addr, sizeof(struct in6_addr)); /* Accept multicast from any interface */ multicastRequest.ipv6mr_interface = 0; /* Join the multicast address */ if ( setsockopt(sfd, IPPROTO_IPV6, IPV6_JOIN_GROUP, (char*) &multicastRequest, sizeof(multicastRequest)) != 0 ) { printf("setsockopt() failed: %d\n", WSAGetLastError()); return -1; } on = 1; if (setsockopt (sfd, IPPROTO_IPV6, IPV6_MULTICAST_IF, (char *)&on, sizeof (on)) == -1) { printf("setsockopt error:%d\n", WSAGetLastError()); return 0; } } memset(buf, 0, sizeof(buf)); strcpy(buf, "hello world"); iResult = sendto(sfd, buf, strlen(buf), 0, (LPSOCKADDR) multicastAddr->ai_addr, multicastAddr->ai_addrlen); if (iResult == SOCKET_ERROR) { printf("setsockopt error:%d\n", WSAGetLastError()); return -1; /* Error handling */ } return 0; }

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• Calculate the number of ways to roll a certain number

  - by helloworld

  I'm a high school Computer Science student, and today I was given a problem to: Program Description: There is a belief among dice players that in throwing three dice a ten is easier to get than a nine. Can you write a program that proves or disproves this belief? Have the computer compute all the possible ways three dice can be thrown: 1 + 1 + 1, 1 + 1 + 2, 1 + 1 + 3, etc. Add up each of these possibilities and see how many give nine as the result and how many give ten. If more give ten, then the belief is proven. I quickly worked out a brute force solution, as such int sum,tens,nines; tens=nines=0; for(int i=1;i<=6;i++){ for(int j=1;j<=6;j++){ for(int k=1;k<=6;k++){ sum=i+j+k; //Ternary operators are fun! tens+=((sum==10)?1:0); nines+=((sum==9)?1:0); } } } System.out.println("There are "+tens+" ways to roll a 10"); System.out.println("There are "+nines+" ways to roll a 9"); Which works just fine, and a brute force solution is what the teacher wanted us to do. However, it doesn't scale, and I am trying to find a way to make an algorithm that can calculate the number of ways to roll n dice to get a specific number. Therefore, I started generating the number of ways to get each sum with n dice. With 1 die, there is obviously 1 solution for each. I then calculated, through brute force, the combinations with 2 and 3 dice. These are for two: There are 1 ways to roll a 2 There are 2 ways to roll a 3 There are 3 ways to roll a 4 There are 4 ways to roll a 5 There are 5 ways to roll a 6 There are 6 ways to roll a 7 There are 5 ways to roll a 8 There are 4 ways to roll a 9 There are 3 ways to roll a 10 There are 2 ways to roll a 11 There are 1 ways to roll a 12 Which looks straightforward enough; it can be calculated with a simple linear absolute value function. But then things start getting trickier. With 3: There are 1 ways to roll a 3 There are 3 ways to roll a 4 There are 6 ways to roll a 5 There are 10 ways to roll a 6 There are 15 ways to roll a 7 There are 21 ways to roll a 8 There are 25 ways to roll a 9 There are 27 ways to roll a 10 There are 27 ways to roll a 11 There are 25 ways to roll a 12 There are 21 ways to roll a 13 There are 15 ways to roll a 14 There are 10 ways to roll a 15 There are 6 ways to roll a 16 There are 3 ways to roll a 17 There are 1 ways to roll a 18 So I look at that, and I think: Cool, Triangular numbers! However, then I notice those pesky 25s and 27s. So it's obviously not triangular numbers, but still some polynomial expansion, since it's symmetric. So I take to Google, and I come across this page that goes into some detail about how to do this with math. It is fairly easy(albeit long) to find this using repeated derivatives or expansion, but it would be much harder to program that for me. I didn't quite understand the second and third answers, since I have never encountered that notation or those concepts in my math studies before. Could someone please explain how I could write a program to do this, or explain the solutions given on that page, for my own understanding of combinatorics? EDIT: I'm looking for a mathematical way to solve this, that gives an exact theoretical number, not by simulating dice

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• Segmentation fault, shared library

  - by user1306184

  I get Segmentation Fault when I try to run my program. Can someone please help me find out what Im doing wrong? Compiling with this: g++ sms_out.cpp -o sms_out g++ -c -fPIC SMSDispatch.cpp g++ -shared SMSDispatch.o -o libSMSDispatch.so It should be a shared library and dynamic linking. I get Segmentation Fault when I try to run sms_out. //sms_out.cpp #include <iostream> #include<cstdlib> #include<fstream> #include<sstream> #include<string> #include "SMSDispatch.h" using namespace std; string sms = ""; void sendSMS(string sms) { SMSDispatch* sPtr=0; sPtr->sendSMS(sms); } int main(int argc, char *argv[]) { if(argv[1]) { string input = argv[1]; string test = "--author"; if(input == test) { cout << "s149113" << endl; return 0; } } string line = ""; string file = "sms_out.txt"; ifstream myfile(file.c_str()); while(getline(myfile, line)) { string idnr, landcode, number, error; istringstream linestream(line); unsigned short errorcode; //Split the sentence getline(linestream, idnr, '\t'); getline(linestream, landcode, ':'); getline(linestream, number, '\t'); getline(linestream, error); if(idnr == "") break; //Make string to int try { errorcode = atoi(error.c_str() ); } catch (exception &) { } //Put together landcode and tlfnumber string nr = landcode + number; string txt = "Thank you for your vote!"; if(errorcode == 100) txt = "Invalid question, please try again"; else if(errorcode == 110) txt = "Sorry, only one vote pr. number"; else if(errorcode == 200) txt = "Invalid alternative, please try again"; else if(errorcode == 300) txt = "Missing a statement after other, please try again"; else if(errorcode == 999) txt = "An error occurred, please try again"; sms += "{\"ID\":" + idnr + ",\"nr\":" + nr + ",\"txt\":" + "\"" + txt + "\"" + "}\n"; } cout << sms << endl; sendSMS(sms); } //SMSDispatch.h #include <string> #ifndef SMSDISPATCH_H #define SMSDISPATCH_H using namespace std; class SMSDispatch{ public: virtual void sendSMS(string json); }; #endif //SMSDispatch.cpp #include <iostream> #include <fstream> #include "SMSDispatch.h" using namespace std; /*virtual*/void SMSDispatch::sendSMS(string json) { ofstream myfile; myfile.open ("sms_out.log"); myfile << json; myfile.close(); } int main() { }

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• customizing into a reusable component in flex

  - by Fresher4Flex

  need to make a reusable custom component from the existing code here. So that I can use this code to make this effect(view stack) to work in any direction. In the code it has user specified height and works from downside. I need to make this component customizable, something like user is able do it in any direction.I need it urgently. I appreciate your help. 1)main Application: <?xml version="1.0" encoding="utf-8"?> <mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" xmlns:sh="windowShade.*"> <sh:Shade id="i1" height="15" headerHeight="14" thisHeight="215" alwaysOnTop="false" y="{this.height - 14}"/> </mx:WindowedApplication> 2)Custom Comp: Shade.mxml <?xml version="1.0" encoding="utf-8"?> <mx:VBox xmlns:mx="http://www.adobe.com/2006/mxml" width="100%" height="300" creationComplete="init()" verticalScrollPolicy="off" verticalGap="0" > <mx:Script> <![CDATA[ import mx.core.Container; import mx.core.Application; import mx.controls.Alert; import mx.effects.easing.*; import mx.binding.utils.BindingUtils; /** * Need host to adjust this object to Top */ public var alwaysOnTop:Boolean = false; /** * User can custom the height of this component */ public var thisHeight:int = 0; /** * User can custom the header height of this component */ [Bindable] public var headerHeight:int = 14; /** * The bindable value of this height */ [Bindable] public var tHeight:int = 0; /** * The bindable value of parent height */ [Bindable] public var pHeight:int = 0; /** * Initialize method */ private function init():void { if (this.thisHeight > 0 ) this.height = this.thisHeight; BindingUtils.bindProperty(this, "tHeight",this,"height" ); BindingUtils.bindProperty(this, "pHeight",this.parent,"height" ); } /** * Toggle button */ private function toggleBtn(e:MouseEvent):void { if (this.alwaysOnTop) { var container:Container = Application.application as Container; container.setChildIndex(this.parent, container.numChildren - 1 ); } if ( vs.selectedIndex == 0 ) panelOut.play(); else panelIn.play(); } ]]> </mx:Script> <mx:Move id="panelOut" target="{this}" yTo="{ pHeight - this.tHeight }" effectEnd="vs.selectedIndex = 1" duration="600" easingFunction="Back.easeOut"/> <mx:Move id="panelIn" target="{this}" yTo="{ this.pHeight - headerHeight }" effectEnd="vs.selectedIndex = 0" duration="600" easingFunction="Back.easeIn"/> <mx:VBox horizontalAlign="center" width="100%"> <mx:ViewStack id="vs" width="100%"> <mx:VBox horizontalAlign="center" > <mx:Label text="VBox 1"/> <mx:Image source="@Embed('/windowShade/add.png')" click="toggleBtn(event)"/> </mx:VBox> <mx:VBox horizontalAlign="center"> <mx:Label text="2nd VBox"/> <mx:Image source="@Embed('/windowShade/back.png')" click="toggleBtn(event)"/> </mx:VBox> </mx:ViewStack> </mx:VBox> <mx:VBox id="drawer" height="100%" width="100%" backgroundColor="#000000"> </mx:VBox> </mx:VBox>

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• Programmatically adding an object and selecting the correspondig row does not make it become the CurrentRow

  - by Robert

  I'm in a struggle with the DataGridView: I do have a BindingList of some simple objects that implement INotifyPropertyChanged. The DataGridView's datasource is set to this BindingList. Now I need to add an object to the list by hitting the "+" key. When an object is added, it should appear as a new row and it shall become the current row. As the CurrentRow-property is readonly, I iterate through all rows, check if its bound item is the newly created object, and if it is, I set this row to "Selected = true;" The problem: although the new object and thereby a new row gets inserted and selected in the DataGridView, it still is not the CurrentRow! It does not become the CurrentRow unless I do a mouse click into this new row. In this test program you can add new objects (and thereby rows) with the "+" key, and with the "i" key the data-bound object of the CurrentRow is shown in a MessageBox. How can I make a newly added object become the CurrentObject? Thanks for your help! Here's the sample: using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Threading.Tasks; using System.Windows.Forms; namespace WindowsFormsApplication1 { public partial class Form1 : Form { BindingList<item> myItems; public Form1() { InitializeComponent(); myItems = new BindingList<item>(); for (int i = 1; i <= 10; i++) { myItems.Add(new item(i)); } dataGridView1.DataSource = myItems; } public void Form1_KeyDown(object sender, KeyEventArgs e) { if (e.KeyCode == Keys.Add) { addItem(); } } public void addItem() { item i = new item(myItems.Count + 1); myItems.Add(i); foreach (DataGridViewRow dr in dataGridView1.Rows) { if (dr.DataBoundItem == i) { dr.Selected = true; } } } private void btAdd_Click(object sender, EventArgs e) { addItem(); } private void dataGridView1_KeyDown(object sender, KeyEventArgs e) { if (e.KeyCode == Keys.Add) { addItem(); } if (e.KeyCode == Keys.I) { MessageBox.Show(((item)dataGridView1.CurrentRow.DataBoundItem).title); } } } public class item : INotifyPropertyChanged { public event PropertyChangedEventHandler PropertyChanged; private int _id; public int id { get { return _id; } set { this.title = "This is item number " + value.ToString(); _id = value; InvokePropertyChanged(new PropertyChangedEventArgs("id")); } } private string _title; public string title { get { return _title; } set { _title = value; InvokePropertyChanged(new PropertyChangedEventArgs("title")); } } public item(int id) { this.id = id; } #region Implementation of INotifyPropertyChanged public void InvokePropertyChanged(PropertyChangedEventArgs e) { PropertyChangedEventHandler handler = PropertyChanged; if (handler != null) handler(this, e); } #endregion } }

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• How to call virtual function of an object in C++

  - by SoonDead

  I'm struggling with calling a virtual function in C++. I'm not experienced in C++, I mainly use C# and Java so I might have some delusions, but bear with me. I have to write a program where I have to avoid dynamic memory allocation if possible. I have made a class called List: template <class T> class List { public: T items[maxListLength]; int length; List() { length = 0; } T get(int i) const { if (i >= 0 && i < length) { return items[i]; } else { throw "Out of range!"; } }; // set the value of an already existing element void set(int i, T p) { if (i >= 0 && i < length) { items[i] = p; } else { throw "Out of range!"; } } // returns the index of the element int add(T p) { if (length >= maxListLength) { throw "Too many points!"; } items[length] = p; return length++; } // removes and returns the last element; T pop() { if (length > 0) { return items[--length]; } else { throw "There is no element to remove!"; } } }; It just makes an array of the given type, and manages the length of it. There is no need for dynamic memory allocation, I can just write: List<Object> objects; MyObject obj; objects.add(obj); MyObject inherits form Object. Object has a virtual function which is supposed to be overridden in MyObject: struct Object { virtual float method(const Input& input) { return 0.0f; } }; struct MyObject: public Object { virtual float method(const Input& input) { return 1.0f; } }; I get the elements as: objects.get(0).method(asdf); The problem is that even though the first element is a MyObject, the Object's method function is called. I'm guessing there is something wrong with storing the object in an array of Objects without dynamically allocating memory for the MyObject, but I'm not sure. Is there a way to call MyObject's method function? How? It's supposed to be a heterogeneous collection btw, so that's why the inheritance is there in the first place. If there is no way to call the MyObject's method function, then how should I make my list in the first place?

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• How can I draw a line with a variable of width?

  - by user1729944

  #include <iostream> #include <cmath> #include "graph1.h" using namespace std; int main() { int diameter = 0; int height = 0; double rate = 0; char repeat = 'y'; int obj_num = 0; displayGraphics(); obj_num = drawRect(0,0,50,400); setColor(obj_num,200,200,200); obj_num = drawRect(0,400,640,79); setColor(obj_num,71,35,35); obj_num = drawLine(50,50,150,50,5); setColor(obj_num,80,80,80); displayBMP("faucet.bmp",150,12); do { do { cout << "Enter the diamater of the cylinder <in inches > 0 but <= 300: "; cin >> diameter; if((diameter<0) || (diameter>300)) { cout << "Incorrect diamater entered; value must be between 1 and 300" << endl; } }while((diameter<0) || (diameter>300)); do { cout << "Enter the height of the cylinder <in inches > 0 but <= 325: "; cin >> height; if((height<0) || (height>325)) { cout << "Incorrect height entered; value must be between 1 and 325" << endl; } }while((height<0) || (height>325)); do { cout << "Enter the facet water's rate: <gallons/minute> "; cin >> rate; if((rate<0) || (rate>100)) { cout << "Incorrect rate entered; value must be between 1 and 100" << endl; } }while((rate<0) || (rate>100)); //I need to draw the lines here. The graphics window has a faucet that is supposed to fill //up a cylinder made out of 3 lines. I don't know how to make the lines vary from the users //input since lines are hard coded with points and all i am receiving is the width for the //bottom line and the height for the left and right lines. cout << "Repeat program? (y/n): "; cin >> repeat; clearGraphics(); }while ( (repeat == 'y') || (repeat == 'Y') ); return 0; } Here is a screenshot for reference:

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• Android - determine specific locations (X,Y coordinates) on a Bitmap on different resolutions?

  - by Mike

  My app that I am trying to create is a board game. It will have one bitmap as the board and pieces that will move to different locations on the board. The general design of the board is square, has a certain number of columns and rows and has a border for looks. Think of a chess board or scrabble board. Before using bitmaps, I first created the board and boarder by manually drawing it - drawLine & drawRect. I decided how many pixels in width the border would be based on the screen width and height passed in on "onSizeChanged". The remaining screen I divided by the number of columns or rows I needed. For examples sake, let's say the screen dimensions are 102 x 102. I may have chosen to set the border at 1 and set the number of rows & columns at 10. That would leave 100 x 100 left (reduced by two to account for the top & bottom border, as well as left/right border). Then with columns and rows set to 10, that would leave 10 pixels left for both height and width. No matter what screen size is passed in, I store exactly how many pixels in width the boarder is and the height & width of each square on the board. I know exactly what location on the screen to move the pieces to based on a simple formula and I know exactly what cell a user touched to make a move. Now how does that work with bitmaps? Meaning, if I create 3 different background bitmaps, once for each density, won't they still be resized to fit each devices screen resolution, because from what I read there were not just 3 screen resolutions, but 5 and now with tablets - even more. If I or Android scales the bitmaps up or down to fit the current devices screen size, how will I know how wide the border is scaled to and the dimensions of each square in order to figure out where to move a piece or calculate where a player touched. So far the examples I have looked at just show how to scale the overall bitmap and get the overall bitmaps width and height. But, I don't see how to tell how many pixels wide or tall each part of the board would be after it was scaled. When I draw each line and rectangle myself based in the screen dimensions from onSizeChanged, I always know these dimensions. If anyone has any sample code or a URL to point me to that I can a read about this with bitmaps, I would appreciate it. Thanks, --Mike BTW, here is some sample code (very simplified) on how I know the dimensions of my game board (border and squares) no matter the screen size. Now I just need to know how to do this with the board as a bitmap that gets scaled to any screen size. @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { intScreenWidth = w; intScreenHeight = h; // Set Border width - my real code changes this value based on the dimensions of w // and h that are passed in. In other words bigger screens get a slightly larger // border. intOuterBorder = 1; /** Reserve part of the board for the boardgame and part for player controls & score My real code forces this to be square, but this is good enough to get the point across. **/ floatBoardHeight = intScreenHeight / 4 * 3; // My real code actually causes floatCellWidth and floatCellHeight to // be equal (Square). floatCellWidth = (intScreenWidth - intOuterBorder * 2 ) / intNumColumns; floatCellHeight = (floatBoardHeight - intOuterBorder * 2) / intNumRows; super.onSizeChanged(w, h, oldw, oldh); }

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• Two functions working but not when I put them together

  - by Error_404

  I'm really new to C(I have been learning Cuda and wanted to learn C so I can run everything together instead of generating data in Java/Python and copy/pasting it manually to my Cuda program to play with). I am trying to open a large file(20+gb) and parse some data but because I was having problems I decided to try to break down my problem first to verify I can open and read line by line a file and then in another file take a sample of the output of a line and try to parse it, then if all goes well I can simply bring them together. I managed(after a bit of a struggle) to get each part working but when I combine them together it doesn't work(I tried in both eclipse & QT creator. QT creator says it exited unexpectedly and eclipse just stops..). Here's the parsing part(it works exactly as I want): #include <string.h> #include <stdio.h> int main() { char line[1024] = "[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 4],"; size_t len = strlen(line); memmove(line, line+1, len-3); line[len-3] = 0; printf("%s \n",line); char str[100], *s = str, *t = NULL; strcpy(str, line); while ((t = strtok(s, " ,")) != NULL) { s = NULL; printf(":%s:\n", t); } return 0; } The data in variable line is exactly as I get if I print each line of a file. But when I copy/paste it into my main program then it doesn't work(QT shows nothing and eclipse just shows the first line). This code is just a few file IO commands that are wrapped around the commands above(everything within the while loop is the exact same as above) #include <stdio.h> #include <stdlib.h> int main() { char line[1024]; FILE *fp = fopen("/Users/me/Desktop/output.txt","r"); printf("Starting.. \n"); int count = 0; int list[30]; //items will be stored here while(fgets(line, 1024, fp) != NULL){ count++; //char line[1024] = "[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 4],"; size_t len = strlen(line); memmove(line, line+1, len-3); line[len-3] = 0; printf("%s \n",line); char str[100], *s = str, *t = NULL; strcpy(str, line); while ((t = strtok(s, " ,")) != NULL) { s = NULL; printf(":%s:\n", t); } } printf(" num of lines is %i \n", count); return 0; } eclipse output: Starting.. 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 4 I can't figure out what I'm doing wrong. I'm using a mac with gcc 4.2, if that helps. The only thing I can think of is maybe I'm doing something wrong the way I parse the list variable so its not accessible later on(I'm not sure its a wild guess). Is there anything I'm missing?

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• Trying to packetize TCP with non-blocking IO is hard! Am I doing something wrong?

  - by Ricket

  Oh how I wish TCP was packet-based like UDP is! But alas, that's not the case, so I'm trying to implement my own packet layer. Here's the chain of events so far (ignoring writing packets) Oh, and my Packets are very simply structured: two unsigned bytes for length, and then byte[length] data. (I can't imagine if they were any more complex, I'd be up to my ears in if statements!) Server is in an infinite loop, accepting connections and adding them to a list of Connections. PacketGatherer (another thread) uses a Selector to figure out which Connection.SocketChannels are ready for reading. It loops over the results and tells each Connection to read(). Each Connection has a partial IncomingPacket and a list of Packets which have been fully read and are waiting to be processed. On read(): Tell the partial IncomingPacket to read more data. (IncomingPacket.readData below) If it's done reading (IncomingPacket.complete()), make a Packet from it and stick the Packet into the list waiting to be processed and then replace it with a new IncomingPacket. There are a couple problems with this. First, only one packet is being read at a time. If the IncomingPacket needs only one more byte, then only one byte is read this pass. This can of course be fixed with a loop but it starts to get sorta complicated and I wonder if there is a better overall way. Second, the logic in IncomingPacket is a little bit crazy, to be able to read the two bytes for the length and then read the actual data. Here is the code, boiled down for quick & easy reading: int readBytes; // number of total bytes read so far byte length1, length2; // each byte in an unsigned short int (see getLength()) public int getLength() { // will be inaccurate if readBytes < 2 return (int)(length1 << 8 | length2); } public void readData(SocketChannel c) { if (readBytes < 2) { // we don't yet know the length of the actual data ByteBuffer lengthBuffer = ByteBuffer.allocate(2 - readBytes); numBytesRead = c.read(lengthBuffer); if(readBytes == 0) { if(numBytesRead >= 1) length1 = lengthBuffer.get(); if(numBytesRead == 2) length2 = lengthBuffer.get(); } else if(readBytes == 1) { if(numBytesRead == 1) length2 = lengthBuffer.get(); } readBytes += numBytesRead; } if(readBytes >= 2) { // then we know we have the entire length variable // lazily-instantiate data buffers based on getLength() // read into data buffers, increment readBytes // (does not read more than the amount of this packet, so it does not // need to handle overflow into the next packet's data) } } public boolean complete() { return (readBytes > 2 && readBytes == getLength()+2); } Basically I need feedback on my code. Please suggest any improvements. Even overhauling my entire system would be okay, if you have suggestions for how better to implement the whole thing. Book recommendations are welcome too; I love books. I just get the feeling that something isn't quite right.

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• c++ protected pointer member to the same class and access privileges

  - by aajmakin

  Hi, Example code is included at the bottom of the message. I'm puzzled about the protected access specifier in a class. I have define a class node which has a protected string member name string name; and a vector of node pointers vector args; Before I thought that a member function of node could not do args[0]-name but a program that does just this does compile and run. However, now I would like to inherit this class and access the name field in one of the args array pointers from this derived class args[0]-name but this does not compile. When I compile the example code below with the commented sections uncommented, the compiler reports: Compiler output: g++ test.cc -o test test.cc: In member function 'void foo::newnode::print_args2()': test.cc:22: error: 'std::string foo::node::name' is protected test.cc:61: error: within this context Compilation exited abnormally with code 1 at Thu Jun 17 12:40:12 Questions: Why can I access the name field of the node pointers in args in class node, because this is what I would excpect from a similarly defined private field in Java. How can I access those fields from the derived class. Example code: #include <iostream> #include <vector> using namespace std; namespace foo { class node; typedef std::vector<node*> nodes; class node { public: node (string _name); void print_args (); void add_node (node* a); protected: nodes args; string name; }; } foo::node::node (string _name) : args(0) { name = _name; } void foo::node::add_node (node* a) { args.push_back(a); } void foo::node::print_args () { for (int i = 0; i < args.size(); i++) { cout << "node " << i << ": " << args[i]->name << endl; } } // namespace foo // { // class newnode : public node // { // public: // newnode (string _name) : node(_name) {} // void print_args2 (); // protected: // }; // } // void foo::newnode::print_args2 () // { // for (int i = 0; i < args.size(); i++) // { // cout << "node " << i << ": " << args[i]->name << endl; // } // } int main (int argc, char** argv) { foo::node a ("a"); foo::node b ("b"); foo::node c ("c"); a.add_node (&b); a.add_node (&c); a.print_args (); // foo::newnode newa ("newa"); // foo::newnode newb ("newb"); // foo::newnode newc ("newc"); // newa.add_node (&newb); // newa.add_node (&newc); // newa.print_args2 (); return 0; }

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• Java JNI leak in c++ process.

  - by user662056

  Hi all.. I am beginner in Java. My problem is: I am calling a Java class's method from c++. For this i am using JNI. Everythings works correct, but i have some memory LEAKS in the process of c++ program... So.. i did simple example.. 1) I create a java machine (jint res = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);) 2) then i take a pointer on java class (jclass cls = env-FindClass("test_jni")); 3) after that i create a java class object object, by calling the constructor (testJavaObject = env-NewObject(cls, testConstruct);) AT THIS very moment in the process of c++ program is allocated 10 MB of memory 4) Next i delete the class , the object, and the Java Machine .. AT THIS very moment the 10 MB of memory are not free ................. So below i have a few lines of code c++ program void main() { { //Env JNIEnv *env; // java virtual machine JavaVM *jvm; JavaVMOption* options = new JavaVMOption[1]; //class paths options[0].optionString = "-Djava.class.path=C:/Sun/SDK/jdk/lib;D:/jms_test/java_jni_leak;"; // other options JavaVMInitArgs vm_args; vm_args.version = JNI_VERSION_1_6; vm_args.options = options; vm_args.nOptions = 1; vm_args.ignoreUnrecognized = false; // alloc part of memory (for test) before CreateJavaVM char* testMem0 = new char[1000]; for(int i = 0; i < 1000; ++i) testMem0[i] = 'a'; // create java VM jint res = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args); // alloc part of memory (for test) after CreateJavaVM char* testMem1 = new char[1000]; for(int i = 0; i < 1000; ++i) testMem1[i] = 'b'; //Creating java virtual machine jclass cls = env->FindClass("test_jni"); // Id of a class constructor jmethodID testConstruct = env->GetMethodID(cls, "<init>", "()V"); // The Java Object // Calling the constructor, is allocated 10 MB of memory in c++ process jobject testJavaObject = env->NewObject(cls, testConstruct); // function DeleteLocalRef, // In this very moment memory not free env->DeleteLocalRef(testJavaObject); env->DeleteLocalRef(cls); // 1!!!!!!!!!!!!! res = jvm->DestroyJavaVM(); delete[] testMem0; delete[] testMem1; // In this very moment memory not free. TO /// } int gg = 0; } java class (it just allocs some memory) import java.util.*; public class test_jni { ArrayList<String> testStringList; test_jni() { System.out.println("start constructor"); testStringList = new ArrayList<String>(); for(int i = 0; i < 1000000; ++i) { // ??????? ?????? testStringList.add("TEEEEEEEEEEEEEEEEST"); } } } process memory view, after crating javaVM and java object: testMem0 and testMem1 - test memory, that's allocated by c++. ************** testMem0 ************** JNI_CreateJavaVM ************** testMem1 ************** // create java object jobject testJavaObject = env->NewObject(cls, testConstruct); ************** process memory view, after destroy javaVM and delete ref on java object: testMem0 and testMem1 are deleted to; ************** JNI_CreateJavaVM ************** // create java object jobject testJavaObject = env->NewObject(cls, testConstruct); ************** So testMem0 and testMem1 is deleted, But JavaVM and Java object not.... Sow what i do wrong... and how i can free memory in the c++ process program.

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• antlr line after line processing

  - by pawloch

  I'm writing simple language in ANTLR, and I'd like to write shell where I can put line of code, hit ENTER and have it executed, enter another line, and have it executed. I have already written grammar which execute all alines of input at one. Example input: int a,b,c; string d; string e; d=\"dziala\"; a=4+7; b=a+33; c=(b/11)*2; grammar Kalkulator; options { language = Java; output=AST; ASTLabelType=CommonTree; } tokens { NEG; } @header { package lab4; } @lexer::header { package lab4; } line : (assignment | declaration)* EOF ; declaration : type^ IDENT (','! IDENT)* ';'! ; type : 'int' | 'string' ; assignment : IDENT '='^ expression ';'! ; term : IDENT | INTEGER | STRING_LITERAL | '('! expression ')'! ; unary : (( negation^ | '+'! ))* term ; negation : '-' -> NEG ; mult : unary ( ('*'^ | '/'^) unary )* ; exp2 :mult ( ('-'^ | '+'^) mult)* ; expression : exp2 ('&'^ exp2)* ; fragment LETTER : ('a'..'z'|'A'..'Z'); fragment DIGIT : '0'..'9'; INTEGER : DIGIT+; IDENT : LETTER (LETTER | DIGIT)* ; WS : (' ' | '\t' | '\n' | '\r' | '\f')+ {$channel=HIDDEN;}; STRING_LITERAL : '\"' .* '\"'; and: tree grammar Evaluator; options { language = Java; tokenVocab = Kalkulator; ASTLabelType = CommonTree; } @header { package lab4; import java.util.Map; import java.util.HashMap; } @members { private Map<String, Object> zmienne = new HashMap<String, Object>(); } line returns [Object result] : (declaration | assignment { result = $assignment.result; })* EOF ; declaration : ^(type ( IDENT { if("string".equals($type.result)){ zmienne.put($IDENT.text,""); //add definition } else{ zmienne.put($IDENT.text,0); //add definition } System.out.println($type.result + " " + $IDENT.text);//write output } )* ) ; assignment returns [Object result] : ^('=' IDENT e=expression) { if(zmienne.containsKey($IDENT.text)) {zmienne.put($IDENT.text, e); result = e; System.out.println(e); } else{ System.out.println("Blad: Niezadeklarowana zmienna"); } } ; type returns [Object result] : 'int' {result="int";}| 'string' {result="string";} ; expression returns [Object result] : ^('+' op1=expression op2=expression) { result = (Integer)op1 + (Integer)op2; } | ^('-' op1=expression op2=expression) { result = (Integer)op1 - (Integer)op2; } | ^('*' op1=expression op2=expression) { result = (Integer)op1 * (Integer)op2; } | ^('/' op1=expression op2=expression) { result = (Integer)op1 / (Integer)op2; } | ^('%' op1=expression op2=expression) { result = (Integer)op1 \% (Integer)op2; } | ^('&' op1=expression op2=expression) { result = (String)op1 + (String)op2; } | ^(NEG e=expression) { result = -(Integer)e; } | IDENT { result = zmienne.get($IDENT.text); } | INTEGER { result = Integer.parseInt($INTEGER.text); } | STRING_LITERAL { String t=$STRING_LITERAL.text; result = t.substring(1,t.length()-1); } ; Can I make it process line-by-line or is that easier to make it all again?

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• std::basic_string full specialization (g++ conflict)

  - by SoapBox

  I am trying to define a full specialization of std::basic_string< char, char_traits<char>, allocator<char> > which is typedef'd (in g++) by the <string> header. The problem is, if I include <string> first, g++ sees the typedef as an instantiation of basic_string and gives me errors. If I do my specialization first then I have no issues. I should be able to define my specialization after <string> is included. What do I have to do to be able to do that? My Code: #include <bits/localefwd.h> //#include <string> // <- uncommenting this line causes compilation to fail namespace std { template<> class basic_string< char, char_traits<char>, allocator<char> > { public: int blah() { return 42; } size_t size() { return 0; } const char *c_str() { return ""; } void reserve(int) {} void clear() {} }; } #include <string> #include <iostream> int main() { std::cout << std::string().blah() << std::endl; } The above code works fine. But, if I uncomment the first #include <string> line, I get the following compiler errors: blah.cpp:7: error: specialization of ‘std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ after instantiation blah.cpp:7: error: redefinition of ‘class std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ /usr/include/c++/4.4/bits/stringfwd.h:52: error: previous definition of ‘class std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ blah.cpp: In function ‘int main()’: blah.cpp:22: error: ‘class std::string’ has no member named ‘blah’ Line 52 of /usr/include/c++/4.4/bits/stringfwd.h: template<typename _CharT, typename _Traits = char_traits<_CharT>, typename _Alloc = allocator<_CharT> > class basic_string; As far as I know this is just a forward delcaration of the template, NOT an instantiation as g++ claims. Line 56 of /usr/include/c++/4.4/bits/stringfwd.h: typedef basic_string<char> string; As far as I know this is just a typedef, NOT an instantiation either. So why are these lines conflicting with my code? What can I do to fix this other than ensuring that my code is always included before <string>?

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• COM port read - Thread remains alive after timeout occurs

  - by Sna

  Hello to all. I have a dll which includes a function called ReadPort that reads data from serial COM port, written in c/c++. This function is called within an extra thread from another WINAPI function using the _beginthreadex. When COM port has data to be read, the worker thread returns the data, ends normaly, the calling thread closes the worker's thread handle and the dll works fine. However, if ReadPort is called without data pending on the COM port, when timeout occurs then WaitForSingleObject returns WAIT_TIMEOUT but the worker thread never ends. As a result, virtual memory grows at about 1 MB every time, physical memory grows some KBs and the application that calls the dll becomes unstable. I also tryied to use TerminateThread() but i got the same results. I have to admit that although i have enough developing experience, i am not familiar with c/c++. I did a lot of research before posting but unfortunately i didn't manage to solve my problem. Does anyone have a clue on how could i solve this problem? However, I really want to stick to this kind of solution. Also, i want to mention that i think i can't use any global variables to use some kind of extra events, because each dll's functions may be called many times for every COM port. I post some parts of my code below: The Worker Thread: unsigned int __stdcall ReadPort(void* readstr){ DWORD dwError; int rres;DWORD dwCommModemStatus, dwBytesTransferred; int ret; char szBuff[64] = ""; ReadParams* params = (ReadParams*)readstr; ret = SetCommMask(params->param2, EV_RXCHAR | EV_CTS | EV_DSR | EV_RLSD | EV_RING); if (ret == 0) { _endthreadex(0); return -1; } ret = WaitCommEvent(params->param2, &dwCommModemStatus, 0); if (ret == 0) { _endthreadex(0); return -2; } ret = SetCommMask(params->param2, EV_RXCHAR | EV_CTS | EV_DSR | EV_RLSD| EV_RING); if (ret == 0) { _endthreadex(0); return -3; } if (dwCommModemStatus & EV_RXCHAR||dwCommModemStatus & EV_RLSD) { rres = ReadFile(params->param2, szBuff, 64, &dwBytesTransferred,NULL); if (rres == 0) { switch (dwError = GetLastError()) { case ERROR_HANDLE_EOF: _endthreadex(0); return -4; } _endthreadex(0); return -5; } else { strcpy(params->param1,szBuff); _endthreadex(0); return 0; } } else { _endthreadex(0); return 0; } _endthreadex(0); return 0;} The Calling Thread: int WINAPI StartReadThread(HANDLE porthandle, HWND windowhandle){ HANDLE hThread; unsigned threadID; ReadParams readstr; DWORD ret, ret2; readstr.param2 = porthandle; hThread = (HANDLE)_beginthreadex( NULL, 0, ReadPort, &readstr, 0, &threadID ); ret = WaitForSingleObject(hThread, 500); if (ret == WAIT_OBJECT_0) { CloseHandle(hThread); if (readstr.param1 != NULL) // Send message to GUI return 0; } else if (ret == WAIT_TIMEOUT) { ret2 = CloseHandle(hThread); return -1; } else { ret2 = CloseHandle(hThread); if (ret2 == 0) return -2; }} Thank you in advance, Sna.

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• Java: how to avoid circual references when dumping object information with reflection?

  - by Tom

  I've modified an object dumping method to avoid circual references causing a StackOverflow error. This is what I ended up with: //returns all fields of the given object in a string public static String dumpFields(Object o, int callCount, ArrayList excludeList) { //add this object to the exclude list to avoid circual references in the future if (excludeList == null) excludeList = new ArrayList(); excludeList.add(o); callCount++; StringBuffer tabs = new StringBuffer(); for (int k = 0; k < callCount; k++) { tabs.append("\t"); } StringBuffer buffer = new StringBuffer(); Class oClass = o.getClass(); if (oClass.isArray()) { buffer.append("\n"); buffer.append(tabs.toString()); buffer.append("["); for (int i = 0; i < Array.getLength(o); i++) { if (i < 0) buffer.append(","); Object value = Array.get(o, i); if (value != null) { if (excludeList.contains(value)) { buffer.append("circular reference"); } else if (value.getClass().isPrimitive() || value.getClass() == java.lang.Long.class || value.getClass() == java.lang.String.class || value.getClass() == java.lang.Integer.class || value.getClass() == java.lang.Boolean.class) { buffer.append(value); } else { buffer.append(dumpFields(value, callCount, excludeList)); } } } buffer.append(tabs.toString()); buffer.append("]\n"); } else { buffer.append("\n"); buffer.append(tabs.toString()); buffer.append("{\n"); while (oClass != null) { Field[] fields = oClass.getDeclaredFields(); for (int i = 0; i < fields.length; i++) { if (fields[i] == null) continue; buffer.append(tabs.toString()); fields[i].setAccessible(true); buffer.append(fields[i].getName()); buffer.append("="); try { Object value = fields[i].get(o); if (value != null) { if (excludeList.contains(value)) { buffer.append("circular reference"); } else if ((value.getClass().isPrimitive()) || (value.getClass() == java.lang.Long.class) || (value.getClass() == java.lang.String.class) || (value.getClass() == java.lang.Integer.class) || (value.getClass() == java.lang.Boolean.class)) { buffer.append(value); } else { buffer.append(dumpFields(value, callCount, excludeList)); } } } catch (IllegalAccessException e) { System.out.println("IllegalAccessException: " + e.getMessage()); } buffer.append("\n"); } oClass = oClass.getSuperclass(); } buffer.append(tabs.toString()); buffer.append("}\n"); } return buffer.toString(); } The method is initially called like this: System.out.println(dumpFields(obj, 0, null); So, basically I added an excludeList which contains all the previousely checked objects. Now, if an object contains another object and that object links back to the original object, it should not follow that object further down the chain. However, my logic seems to have a flaw as I still get stuck in an infinite loop. Does anyone know why this is happening?

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