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  • Accessing structure elements using pointers

    - by Arun Nadesh
    Hi Everybody, Greetings! I got surprised when the following program did not crash. typedef struct _x{ int a; char b; int c; }x; main() { x *ptr=0; char *d=&ptr->b; } As per my understanding the -> operator has higher precedence over & operator. So I expected the program to crash at the below statement when we try to dereference the NULL pointer tr. char *d=&ptr->b; But the statement &ptr->b evaluates to a valid address. Could somebody please explain where I'm wrong? Thanks & Regards, Arun

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  • How do I get around Inconsistant accessibilty error in C # ?

    - by xarzu
    How do I get around Inconsistant accessibilty error in C # ? I need to pass a pointer to a node in a linked list to a method. When I do, I get a "Compiler Error CS0051" Example The following sample generates CS0051: Copy Code // CS0051.cs public class A { // Try making B public since F is public // B is implicitly private here class B { } public static void F(B b) // CS0051 { } public static void Main() { } } That is a simple example. The actual program is a bit more complicated. I am actually using a node in a linked list to pass to the method LinkedListNode node The method uses recursion because the node is mart of a huge linked list structure of linked lists that outputs an xml file. Either I have to find a way to use recursion without using methods or I need to find a way to pass pointers nodes or actual nodes.

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  • Unpacking Argument Lists and Instantiating WTForms objects from web.py

    - by Morris Cornell-Morgan
    After a bit of searching, I've found that it's possible to instantiate a WTForms object in web.py using the following code: form = my_form(**web.input()) web.input() returns a "dictionary-like" web.storage object, but without the double asterisks WTForms will raise an exception: TypeError: formdata should be a multidict-type wrapper that supports the 'getlist' method From the Python documentation I understand that the two asterisks are used to unpack a dictionary of named arguments. That said, I'm still a bit confused about exactly what is going on. What makes the web.storage object returned by web.input() "dictionary-like" enough that it can be unpacked by ** but not "dictionary-like" enough that it can be passed as-is to the WTForms constructor? I know that this is an extremely basic question, but any advice to help a novice programmer would be greatly appreciated!

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  • How to include file outside document root?

    - by Brayn
    Hey, What I want do to is to include 'file1.php' from 'domain1' into 'file2.php' on 'domain2'. So what I figured I should do is something like this: file2.php require_once '/var/www/vhosts/domain1/httpdocs/file1.php'; But this won't work for reasons I can't truly grasp. So what I did was to add my path to the include path. Something like: file2.php set_include_path(get_include_path() . PATH_SEPARATOR . "/var/www/vhosts/domain1/httpdocs"); require_once 'file1.php'; So can you please give me some hints as of where I'm doing wrong ? Thanks UPDATE - Either way I get the following error message: Fatal error: require() [function.require]: Failed opening required '/var/www/vhosts/domain1/httpdocs/file1.php' (include_path='.:/php/includes:/usr/share/pear/') in /var/www/vhosts/domain2/httpdocs/file2.php on line 4 Also I have tried this both with safe_mode On and Off. UPDATE2: Also I've changed the permissions to 777 on my test file and I've double-checked the paths to the include file in bash.

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  • Avoiding Mixup of Language Details

    - by DarenW
    Today someone asked me what was wrong with their source code. It was obvious. "Use double equals in place of that single equal in that if statement. Um, i think..." As i remember some languages actually take a single equals for comparison. Since i sometimes forget or mix up the syntax details among the several languages i use, i stepped over to my laptop to try a quickie experiment... It costs a bit of time and is a break in the flow to try "quick" experiments (though maybe the practice is good for memory.) What tips do you have for keeping straight in your mind the syntax (and other) details of multiple languages? (And nowadays, this applies just as well to the many wiki-like markups!)

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  • Finding the closest grid coordinate to the mouse position with javascript/jQuery

    - by Acorn
    What I'm trying to do is make a grid of invisible coordinates on the page equally spaced. I then want a <div> to be placed at whatever grid coordinate is closest to the pointer when onclick is triggered. Here's the rough idea: I have the tracking of the mouse coordinates and the placing of the <div> worked out fine. What I'm stuck with is how to approach the problem of the grid of coordinates. First of all, should I have all my coordinates in an array which I then compare my onclick coordinate to? Or seeing as my grid coordinates follow a rule, could I do something like finding out which coordinate that is a multiple of whatever my spacing is is closest to the onclick coordinate? And then, where do I start with working out which grid point coordinate is closest? What's the best way of going about it? Thanks!

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  • How was non-decimal money represented in software?

    - by dan04
    A lot of the answers to the questions about the accuracy of float and double recommend the use of decimal for monetary amounts. This works because today all currencies are decimal except MGA and MRO, and those have subunits of 1/5 so are still decimal-friendly. But what about the software used in U.S. stock markets when prices were in 1/16ths of dollar? The accuracy of binary data types wouldn't have been an issue, right? Going further back, how did pre-1971 British accounting software deal with pounds, shillings, and pence? Did their versions of COBOL have a special PIC clause for it? Were all amounts stored in pence? How was decimalisation handled?

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  • improving conversions to binary and back in C#

    - by Saad Imran.
    I'm trying to write a general purpose socket server for a game I'm working on. I know I could very well use already built servers like SmartFox and Photon, but I wan't to go through the pain of creating one myself for learning purposes. I've come up with a BSON inspired protocol to convert the the basic data types, their arrays, and a special GSObject to binary and arrange them in a way so that it can be put back together into object form on the client end. At the core, the conversion methods utilize the .Net BitConverter class to convert the basic data types to binary. Anyways, the problem is performance, if I loop 50,000 times and convert my GSObject to binary each time it takes about 5500ms (the resulting byte[] is just 192 bytes per conversion). I think think this would be way too slow for an MMO that sends 5-10 position updates per second with a 1000 concurrent users. Yes, I know it's unlikely that a game will have a 1000 users on at the same time, but like I said earlier this is supposed to be a learning process for me, I want to go out of my way and build something that scales well and can handle at least a few thousand users. So yea, if anyone's aware of other conversion techniques or sees where I'm loosing performance I would appreciate the help. GSBitConverter.cs This is the main conversion class, it adds extension methods to main datatypes to convert to the binary format. It uses the BitConverter class to convert the base types. I've shown only the code to convert integer and integer arrays, but the rest of the method are pretty much replicas of those two, they just overload the type. public static class GSBitConverter { public static byte[] ToGSBinary(this short value) { return BitConverter.GetBytes(value); } public static byte[] ToGSBinary(this IEnumerable<short> value) { List<byte> bytes = new List<byte>(); short length = (short)value.Count(); bytes.AddRange(length.ToGSBinary()); for (int i = 0; i < length; i++) bytes.AddRange(value.ElementAt(i).ToGSBinary()); return bytes.ToArray(); } public static byte[] ToGSBinary(this bool value); public static byte[] ToGSBinary(this IEnumerable<bool> value); public static byte[] ToGSBinary(this IEnumerable<byte> value); public static byte[] ToGSBinary(this int value); public static byte[] ToGSBinary(this IEnumerable<int> value); public static byte[] ToGSBinary(this long value); public static byte[] ToGSBinary(this IEnumerable<long> value); public static byte[] ToGSBinary(this float value); public static byte[] ToGSBinary(this IEnumerable<float> value); public static byte[] ToGSBinary(this double value); public static byte[] ToGSBinary(this IEnumerable<double> value); public static byte[] ToGSBinary(this string value); public static byte[] ToGSBinary(this IEnumerable<string> value); public static string GetHexDump(this IEnumerable<byte> value); } Program.cs Here's the the object that I'm converting to binary in a loop. class Program { static void Main(string[] args) { GSObject obj = new GSObject(); obj.AttachShort("smallInt", 15); obj.AttachInt("medInt", 120700); obj.AttachLong("bigInt", 10900800700); obj.AttachDouble("doubleVal", Math.PI); obj.AttachStringArray("muppetNames", new string[] { "Kermit", "Fozzy", "Piggy", "Animal", "Gonzo" }); GSObject apple = new GSObject(); apple.AttachString("name", "Apple"); apple.AttachString("color", "red"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)1.5); GSObject lemon = new GSObject(); apple.AttachString("name", "Lemon"); apple.AttachString("color", "yellow"); apple.AttachBool("inStock", false); apple.AttachFloat("price", (float)0.8); GSObject apricoat = new GSObject(); apple.AttachString("name", "Apricoat"); apple.AttachString("color", "orange"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)1.9); GSObject kiwi = new GSObject(); apple.AttachString("name", "Kiwi"); apple.AttachString("color", "green"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)2.3); GSArray fruits = new GSArray(); fruits.AddGSObject(apple); fruits.AddGSObject(lemon); fruits.AddGSObject(apricoat); fruits.AddGSObject(kiwi); obj.AttachGSArray("fruits", fruits); Stopwatch w1 = Stopwatch.StartNew(); for (int i = 0; i < 50000; i++) { byte[] b = obj.ToGSBinary(); } w1.Stop(); Console.WriteLine(BitConverter.IsLittleEndian ? "Little Endian" : "Big Endian"); Console.WriteLine(w1.ElapsedMilliseconds + "ms"); } Here's the code for some of my other classes that are used in the code above. Most of it is repetitive. GSObject GSArray GSWrappedObject

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  • Sending message from working non-gui thread to the main window

    - by bartek
    I'm using WinApi. Is SendMessage/PostMessage a good, thread safe method of communicating with the main window? Suppose, the working thread is creating a bitmap, that must be displayed on the screen. The working thread allocates a bitmap, sends a message with a pointer to this bitmap and waits until GUI thread processes it (for example using SendMessage). The working thread shares no data with other threads. Am I running into troubles with such design? Are there any other possibilities that do not introduce thread synchronizing, locking etc. ?

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  • Passing Boost uBLAS matrices to OpenGL shader

    - by AJM
    I'm writing an OpenGL program where I compute my own matrices and pass them to shaders. I want to use Boost's uBLAS library for the matrices, but I have little idea how to get a uBLAS matrix into OpenGL's shader uniform functions. matrix<GLfloat, column_major> projection(4, 4); // Fill matrix ... GLuint projectionU = glGetUniformLocation(shaderProgram, "projection"); glUniformMatrix4fv(projectionU, 1, 0, (GLfloat *)... Um ...); Trying to cast the matrix to a GLfloat pointer causes an invalid cast error on compile.

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  • What happens to date-times and booleans when using DbLinq with SQLite?

    - by DanM
    I've been thinking about using SQLite for my next project, but I'm concerned that it seems to lack proper datetime and bit data types. If I use DbLinq (or some other ORM) to generate C# classes, will the data types of the properties be "dumbed down"? Will date-time data be placed in properties of type string or double? Will boolean data be placed in properties of type int? If yes, what are the implications? I'm imaging a scenario where I need to write a whole second layer of classes with more specific data types and do a bunch of transformations and casts, but maybe it's not so bad. If you have any experience with this or a similar scenario, what are your "lessons learned"?

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  • How do I copy object in Qt?

    - by Martin
    I'm using Qt and have some real basic problems. I have created my own widget MyTest that have a variable obj. I need to set this variable obj from an object outside of the widget so that the variable is copied not just a pointer to another object. I get an error message and can't figure out how to do this basic stuff. This is the code I'm using: MyTest.h: class MyTest : public QWidget { Q_OBJECT public: void setObj(QObject &inobj); QObject obj; .... } MyTest.cpp: void MyTest::setObj(QObject &inobj) { obj = inobj; //HERE I get the error message: "illegal access from 'QObject' to protected/private member 'QObject::operator=(const QObject &)'" } main.cpp: int main(int argc, char *argv[]) { QApplication a(argc, argv); QObject *ob = new QObject(); MyTest w; w.setObj(*ob); } Thanks for your help!

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  • Put an X on the topright of a div without making the top clickable

    - by acidzombie24
    I have a rect and have an X on the top right with items inside of it. The div with the X is clickable. The problem is the whole top area is clickable and not just the topright (the 'X') as i wanted. How do i make only the X clickable and still align to the right? my css is .itembox { float:left; } .itembox .RemoveMediaNotif { text-align: right; text-decoration:underline; cursor: pointer; } my html is <div class="itembox" id="i16"><div class="RemoveMediaNotif">X</div><div ...

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  • Django excluding specific instances from queryset without using field lookup

    - by Agos
    Hi, I sometimes have the need to make sure some instances are excluded from a queryset. This is the way I do it usually: unwanted_instance = Mymodel.objects.get(pk=bad_luck_number) uninteresting_stuff_happens() my_results = MyModel.objects.exclude(id=unwanted_instance.id) or, if I have more of them: my_results = MyModel.objects.exclude(id_in=[uw_in1.id, uw_in2.id, uw_in3.id]) This 'feels' a bit clunky, so I tried if I was lucky: my_ideally_obtained_results = MyModel.objects.exclude(unwanted_instance) Which doesn't work. But I read here on SO that a subquery can be used as parameter for exclude. Am I out of luck? Am I missing some functionality (checked the docs, but didn't find any useful pointer)

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  • Is it possible to run a MIDP application under Android

    - by SteveM
    The Google Market offers an application purporting to run J2ME MIDP applications on the Nexus One. I have tried this application but it only appears to run MIDP applications that are downloaded from particular web sites; it does not seem capable of picking up a MIDP application that is stored on the SD card in the phone. I have suggested to the developers that they might like to add such functionality, but they have not been particularly responsive to my messages. So I would like to build my own MIDP runner for Android and would like to see if I can find a pointer as to where to start, or even whether this is possible. The MIDP application in question was supplied on CD along with a security camera system and permits remote viewing and remote control over the security system. Clearly it wasn't built with the Android platform in mind. However, if it is possible somehow to run MIDP applications on Android (perhaps by creating some kind of sandbox environment for example) then I'd be quite keen to develop it.

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  • pthread_create from non-static member function

    - by Stanislav Palatnik
    This is somewhat similiar to this : http://stackoverflow.com/questions/1151582/pthread-function-from-a-class But the function that's getting called in the end is referencing the this pointer, so it cannot be made static. void * Server::processRequest() { std::string tmp_request, outRequest; tmp_request = this->readData(); outRequest = this->parse(tmp_request); this->writeReply(outRequest); } void * LaunchMemberFunction(void * obj) { return ((Server *)obj)->processRequest(); } and then the pthread_create pthread_create(&handler[tcount], &attr, (void*)LaunchMemberFunction,(void*)&SServer); errors: SS_Twitter.cpp:819: error: invalid conversion from void* to void* ()(void) SS_Twitter.cpp:819: error: initializing argument 3 of int pthread_create(pthread_t*, const pthread_attr_t*, void* ()(void), void*)

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  • Patterns for simulating optional "out" parameters in C#?

    - by Jesse McGrew
    I'm translating an API from C to C#, and one of the functions allocates a number of related objects, some of which are optional. The C version accepts several pointer parameters which are used to return integer handles to the objects, and the caller can pass NULL for some of the pointers to avoid allocating those objects: void initialize(int *mainObjPtr, int *subObjPtr, int *anotherSubObjPtr); initialize(&mainObj, &subObj, NULL); For the C# version, the obvious translation would use out parameters instead of pointers: public static void Initialize(out int mainObj, out int subObj, out int anotherSubObj); ... but this leaves no way to indicate which objects are unwanted. Are there any well-known examples of C# APIs doing something similar that I could imitate? If not, any suggestions?

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  • printing sequence number of a sniffed packet

    - by scatman
    i am using pcap to create a packet sniffer. i have this tcp structure: typedef struct TSP_header{ unsigned short int sport; unsigned short int dport; unsigned int seqnum; unsigned int acknum; unsigned char reserved:4, offset:4; unsigned int tcp_res1:4, //little-endian tcph_hlen:4, //length of tcp header in 32-bit words tcph_fin:1, //Finish flag "fin" tcph_syn:1, //Synchronize sequence numbers to start a connection tcph_rst:1, //Reset flag tcph_psh:1, //Push, sends data to the application tcph_ack:1, //acknowledge tcph_urg:1, //urgent pointer tcph_res2:2; unsigned short int tcph_win; unsigned short int tcph_chksum; unsigned short int tcph_urgptr; }TSP_header; how can i print the sequence number? shou i use htons(sequence_number)?? coz it isn't working this way!!

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  • C# Reset a property

    - by Jeff
    I'm writing a Clone function for a non serializeable object.For most objects I don't care if they are shallow copied as I won't be making any changes to them. I start with a MemberwiseClone and this copies all the values and few objects like configuration dictionary over just fine but they are pointers. EAVEntity newClone = (EAVEntity) this.MemberwiseClone(); newClone.EntityStorageID = Guid.NewGuid(); newClone.Controls.Clear(); So how do I reset a pointer so I can make them not point at the same location?

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  • How to check if two types can be compared, summed etc.?

    - by Marcus
    Hi, if given two types (Type a, Type b), is there any "nice" way to find out if those two can be compared, summed etc.? I was thinking if the types implement IConvertible, one could convert both to lets say decimal and perform a "Convert.ToDecimal(a) > Convert.ToDecimal(b)" ? I am building an expression evaluator and want to be able to work with any kind of object and thus need to know if a type can be compared to another type (it DOESN'T have to be the same types on both sides. eg. double > int)

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  • regex to match postgresql bytea

    - by filiprem
    In PostgreSQL, there is a BLOB datatype called bytea. It's just an array of bytes. bytea literals are output in the following way: '\\037\\213\\010\\010\\005`Us\\000\\0001.fp3\'\\223\\222%' See PostgreSQL docs for full definition of the format. I'm trying to construct a Perl regular expression which will match any such string. It should also match standard ANSI SQL string literals, like 'Joe', 'Joe''s Mom', 'Fish Called ''Wendy''' It should also match backslash-escaped variant: 'Joe\'s Mom', . First aproach (shown below) works only for some bytea representations. s{ ' # Opening apostrophe (?: # Start group [^\\\'] # Anything but a backslash or an apostrophe | # or \\ . # Backslash and anything | # or \'\' # Double apostrophe )* # End of group ' # Closing apostrophe }{LITERAL_REPLACED}xgo; For other (longer ones, with many escaped apostrophes, Perl gives such warning: Complex regular subexpression recursion limit (32766) exceeded at ./sqa.pl line 33, < line 1. So I am looking for a better (but still regex-based) solution, it probably requires some regex alchemy (avoiding backreferences and all).

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  • C++ min heap with user-defined type.

    - by bsg
    Hi, I am trying to implement a min heap in c++ for a struct type that I created. I created a vector of the type, but it crashed when I used make_heap on it, which is understandable because it doesn't know how to compare the items in the heap. How do I create a min-heap (that is, the top element is always the smallest one in the heap) for a struct type? The struct is below: struct DOC{ int docid; double rank; }; I want to compare the DOC structures using the rank member. How would I do this? I tried using a priority queue with a comparator class, but that also crashed, and it also seems silly to use a data structure which uses a heap as its underlying basis when what I really need is a heap anyway. Thank you very much, bsg

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  • Is there any simple way to test two PNGs for equality?

    - by Mason Wheeler
    I've got a bunch of PNG images, and I'm looking for a way to identify duplicates. By duplicates I mean, specifically, two PNG files whose uncompressed image data are identical, not necessarily whose files are identical. This means I can't do something simple like compare CRC hash values. I figure this can actually be done reliably since PNGs use lossless compression, but I'm worried about speed. I know I can winnow things down a little by testing for equal dimensions first, but when it comes time to actually compare the images against each other, is there any way to do it reasonably efficiently? (ie. faster than the "double-for-loop checking pixel values against each other" brute-force method?)

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  • Prototype Library use of !! operator

    - by Rajat
    Here is a snippet from Prototype Javascript Library : Browser: (function(){ var ua = navigator.userAgent; var isOpera = Object.prototype.toString.call(window.opera) == '[object Opera]'; return { IE: !!window.attachEvent && !isOpera, Opera: isOpera, WebKit: ua.indexOf('AppleWebKit/') > -1, Gecko: ua.indexOf('Gecko') > -1 && ua.indexOf('KHTML') === -1, MobileSafari: /Apple.*Mobile/.test(ua) } })(), This is all good and i understand the objective of creating a browser object. One thing that caught my eye and I haven't been able to figure out is the use of double not operator !! in the IE property. If you read through the code you will find it at many other places. I dont understand whats the difference between !!window.attachEvent and using just window.attachEvent. Is it just a convention or is there more to it that's not obvious?

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  • Throwing Exception in CTOR and Smart Pointers

    - by David Relihan
    Is it OK to have the following code in my constructor to load an XML document into a member variable - throwing to caller if there are any problems: MSXML2::IXMLDOMDocumentPtr m_docPtr; //member Configuration() { try { HRESULT hr = m_docPtr.CreateInstance(__uuidof(MSXML2::DOMDocument40)); if ( SUCCEEDED(hr)) { m_docPtr->loadXML(CreateXML()); } else { //throw exception to caller } } catch(...) { //throw exception to caller } } Based on Scott Myers RAII implementations in More Effective C++ I believe I am alright in just allowing exceptions to be thrown from CTOR as I am using a smart pointer(IXMLDOMDocumentPtr). Let me know what you think....

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