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• C - add elements to struct by define

  - by CodeStepper

  I have a problem. I'm trying to add struct elements by previously defined constant. This is sample code (OpenGL+WinAPI) #define ENGINE_STRUCT \ HGLRC RenderingContext;\ HDC DeviceContext; And then: typedef struct SWINDOW { ENGINE_STRUCT HWND Handle; HINSTANCE Instance; CHAR* ClassName; BOOL Fullscreen; BOOL Active; MSG Message; } WINDOW; Is this possible? Thanks in advance.

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• How to get notified of modification in the memory in Linux

  - by Song Yuan

  In a userspace program in Linux, I get a piece of memory via allocation from the heap, then the pointer is distributed to a lot of other components running in other threads to use. I would like to get notified when the said piece of memory is modified. I can of course develop a custom userspace solution for other components to use when they try to modify the memory. The problem in my case is that these are legacy components and they can write to memory in many occasions. So I'm wondering whether there is a similar API like inotify (get notified when file is changed) or other approaches in order to get notified when a piece of memory is changed. I considered using mmap and inotify, which obviously won't work if the changes are not flushed. Any suggestions are appreciated :-)

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• using arrays to get best memory alignment and cache use, is it necessary?

  - by Alberto Toglia

  I'm all about performance these days cause I'm developing my first game engine. I'm no c++ expert but after some research I discovered the importance of the cache and the memory alignment. Basically what I found is that it is recommended to have memory well aligned specially if you need to access them together, for example in a loop. Now, In my project I'm doing my Game Object Manager, and I was thinking to have an array of GameObjects references. meaning I would have the actual memory of my objects one after the other. static const size_t MaxNumberGameObjects = 20; GameObject mGameObjects[MaxNumberGameObjects]; But, as I will be having a list of components per object -Component based design- (Mesh, RigidBody, Transformation, etc), will I be gaining something with the array at all? Anyway, I have seen some people just using a simple std::map for storing game objects. So what do you guys think? Am I better off using a pure component model?

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• Passing around objects to network packet handlers ?

  - by xeross

  Hey, I've been writing a networking server for a while now in C++ and have come to the stage to start looking for a way to properly and easily handle all packets. I am so far that I can figure out what kind of packet it is, but now I need to figure out how to get the needed data to the handler functions. I had the following in mind: Have a map of function pointers with the opcode as key and the function pointer as value Have all these functions have 2 arguments, packet and ObjectAccessor ObjectAccessor class contains various functions to fetch various items such as users and alike Perhaps pass the user's guid too so we can fetch it from the objectaccessor I'd like to know the various implementations others have come up with, so please comment on this idea and reply with your own implementations. Thanks, Xeross

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• What elegant method callback design should be used ?

  - by ereOn

  Hi, I'm surprised this question wasn't asked before on SO (well, at least I couldn't find it). Have you ever designed a method-callback pattern (something like a "pointer" to a class method) in C++ and, if so, how did you do it ? I know a method is just a regular function with some hidden this parameter to serve as a context and I have a pretty simple design in mind. However, since things are often more complex than they seem to, I wonder how our C++ gurus would implement this, preferably in an elegant and standard way. All suggestions are welcome !

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• += Overloading in C++ problem.

  - by user69514

  I am trying to overload the += operator for my rational number class, but I don't believe that it's working because I always end up with the same result: RationalNumber RationalNumber::operator+=(const RationalNumber &rhs){ int den = denominator * rhs.denominator; int a = numerator * rhs.denominator; int b = rhs.numerator * denominator; int num = a+b; RationalNumber ratNum(num, den); return ratNum; } Inside main //create two rational numbers RationalNumber a(1, 3); a.print(); RationalNumber b(6, 7); b.print(); //test += operator a+=(b); a.print(); After calling a+=(b), a is still 1/3, it should be 25/21. Any ideas what I am doing wrong?

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• Lock thread using somthing other than a object

  - by Scott Chamberlain

  when using a lock does the thing you are locking on have to be a object. For example is this legal static DateTime NextCleanup = DateTime.Now; const TimeSpan CleanupInterval = new TimeSpan(1, 0, 0); private static void DoCleanup() { lock ((object)NextCleanup) { if (NextCleanup < DateTime.Now) { NextCleanup = DateTime.Now.Add(CleanupInterval); System.Threading.ThreadPool.QueueUserWorkItem(new System.Threading.WaitCallback(cleanupThread)); } } return; } EDIT-- From reading SLaks' responce I know the above code would be not valid but would this be? static MyClass myClass = new MyClass(); private static void DoCleanup() { lock (myClass) { // } return; }

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• How is inheritance implemented at the memory level?

  - by cambr

  Suppose I have class A { public: void print(){cout<<"A"; }}; class B: public A { public: void print(){cout<<"B"; }}; class C: public C { }; How is inheritance implemented at the memory level? Does C copy print() code to itself or does it have a pointer to the it that points somewhere in A part of the code? How does the same thing happen when we override the previous definition, for example in B (at the memory level)?

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• Using Boost statechart, how can I transition to a state unconditionally?

  - by nickb

  I have a state A that I would like to transition to its next state B unconditionally, once the constructor of A has completed. Is this possible? I tried posting an event from the constructor, which does not work, even though it compiles. Thanks. Edit: Here is what I've tried so far: struct A : sc::simple_state< A, Active > { public: typedef sc::custom_reaction< EventDoneA > reactions; A() { std::cout << "Inside of A()" << std::endl; post_event( EventDoneA() ); } sc::result react( const EventDoneA & ) { return transit< B >(); } }; This yields the following runtime assertion failure: Assertion failed: get_pointer( pContext_ ) != 0, file /includ e/boost/statechart/simple_state.hpp, line 459

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• function to remove duplicate characters in a string

  - by Codenotguru

  The following code is trying to remove any duplicate characters in a string.Iam not sure if the code is right??Can anybody help me with the working of the code i.e whats actually happening when there is a match in characters? public static void removeDuplicates(char[] str) { if (str == null) return; int len = str.length; if (len < 2) return; int tail = 1; for (int i = 1; i < len; ++i) { int j; for (j = 0; j < tail; ++j) { if (str[i] == str[j]) break; } if (j == tail) { str[tail] = str[i]; ++tail; } } str[tail] = 0; }

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• SQL tables using VARCHAR with UTF8 (with respect to multi byte character length)

  - by Elius

  Like in Oracle VARCHAR( 60 CHAR ) I would like to specify a varchar field with variable length depending on the inserted characters. for example: create table X (text varchar(3)) insert into X (text) VALUES ('äöü') Should be possible (with UTF8 as the default charset of the database). On DB2 I got this Error: DB2 SQL Error: SQLCODE=-302, SQLSTATE=22001 (Character data, right truncation occurred; for example, an update or insert value is a string that is too long for the column, or a datetime value cannot be assigned to a host variable, because it is too small.) I'm looking for solutions for DB2, MsSql, MySql, Hypersonic.

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• Is there any reason for a blocking call to winsock send() function on Vista to return immediately ?

  - by ivymike

  Hi All, Is there any reason for a blocking call to winsock's send() function on Vista to return immediately ? It works with expected delay on XP and below. I'm wondering if this has got anything to do with auto-tuning feature of Vista. Code: char *pBuffer; // pointer to data int bytes; // total size int i = 0, j=0; while (i < bytes) { j = send(m_sock, pBuffer+i, bytes-i, 0); i+=j; } Thanks, Pavan

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• boost timer usage question

  - by stefita

  I have a really simple question, yet I can't find an answer for it. I guess I am missing something in the usage of the boost timer.hpp. Here is my code, that unfortunately gives me an error message: include <boost/timer.hpp> int main() { boost::timer t; } And the error messages are as follows: /usr/include/boost/timer.hpp: In member function ‘double boost::timer::elapsed_max() const’: /usr/include/boost/timer.hpp:59: error: ‘numeric_limits’ is not a member of ‘std’ /usr/include/boost/timer.hpp:59: error: ‘::max’ has not been declared /usr/include/boost/timer.hpp:59: error: expected primary-expression before ‘double’ /usr/include/boost/timer.hpp:59: error: expected `)' before ‘double’ The used library is boost 1.36 (SUSE 11.1). Thanks in advance!

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• Passing arguments to Shared Function - C

  - by SpyrosR

  I have used dlopen to load an object and dlsym to get a function pointer to a shared object function. Everything works fine. I have tested it calling then the shared function which (for now) only prints and it works-prints fine in the main program calling it. Now I want to pass two arguments to this function. An int and a char * .Can anyone help me understand how can I pass arguments to a shared function? I have searched in the web but I cannot understand how it works.

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• BigInteger.ToString() returns more than 50 decimal digits.

  - by brickner

  I'm using .NET 4 System.Numerics.BigInteger Structure and I'm getting results different from the documentation. In the documentation of BigInteger.ToString() Method It says: The ToString() method supports 50 decimal digits of precision. That is, if the BigInteger value has more than 50 digits, only the 50 most significant digits are preserved in the output string; all other digits are replaced with zeros. I have some code that takes a 60 decimal digits BigInteger and converts it to a string. The 60 significant decimal digits string didn't lose any significant digits: const string vString = "123456789012345678901234567890123456789012345678901234567890"; Assert.AreEqual(60, vString.Length); BigInteger v = BigInteger.Parse(vString); Assert.AreEqual(60, v.ToString().Length); Assert.AreEqual('9', v.ToString()[58]); Assert.AreEqual('1', v.ToString()[0]); Assert.AreEqual(vString, v.ToString()); All the asserts pass. What exactly does the quoted part of the documentation mean?

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• Declaring static arrays in php

  - by user220201

  Hi, I am new to php. I was wondering how I could declare a static array in php. Here is what I would do in C. How is the corresponding php code for it? char a[][] = { (1,1), (1,2), (1,3), (2,1), (2,2), (2,3), (3,1), (3,2), (3,3) }; From what I read it has to be something like this - $a = array( 1 = array(1,1), 2 = array(1,2), ... ); Is this correct? If so it sucks :) I hope I am wrong. Thanks, - Pav

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• add different characters to a NSString one by one??

  - by hemant

  i am retrieving different characters from a string by using thsi function and adding 5 to them to display the corresponding character for eg. 'a' displays 'f' and 'h' displays 'm'.. but the problem is that i am not able to add these characters into a string which i can use to display to display like 'fm'...can anyone help?? heres the code strResult(mutablestring) is getting null only. `str=@"John"; int a=[str length]; for(i=0;i char ch=[str characterAtIndex:i]; ch=ch+5; temp=[NSString stringWithFormat:@"%c",ch]; [strResult appendString:temp]; NSLog(@"%c",ch); }`

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• HTAccess mod rewrite issue using QSA

  - by Matt

  Hey, I want to add a parameter to a URL but currently it isnt showing in the $_GET global. A snippet from my htaccess file is as below: RewriteRule ^account/blogs/([0-9]+)/([^\s?]+)/?$ /account/blog.php?blogId=$1 [L,QSA] Then in my php code i want to add a link such as: /account/blogs/1/ThisIsWhereTheTitleGoes?delete=1 The wildcard (any char but space) option is for the blog title as i never know what it would be. I know want to add a query string param on the end such as ?delete=1. I however dont want this as part of the rewrite. Does anybody know how to so this? Thanks

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• Manage bad_alloc exception in C++ construtor

  - by Jimmy zhang

  I have Java experience and recently am doing some C++ coding. My question is that if I have class A, in which I have to instantiate class B and class C as two of the member variables of A. If in the constructor of A, should I assume that allocations of class B and C never fail, and handle the bad allocation exception in the destructor of A? If I don't make that assumption, meaning that I add some try catch block to catch bad_alloc of class B and class C, then if the allocation exception occurs, should I do clean up in the constructor of A? What are the recommended practices? If "new" generates a bad allocation, what value does the pointer carry?

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• Is there any way to pass an anonymous array as an argument in C++?

  - by Jeremy Friesner

  Hi all, I'd like to be able to declare an array as a function argument in C++, as shown in the example code below (which doesn't compile). Is there any way to do this (other than declaring the array separately beforehand)? #include <stdio.h> static void PrintArray(int arrayLen, const int * array) { for (int i=0; i<arrayLen; i++) printf("%i -> %i\n", i, array[i]); } int main(int, char **) { PrintArray(5, {5,6,7,8,9} ); // doesn't compile return 0; }

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• Possible to convert list of #defines into strings (C++)

  - by brandonC

  Suppose I have a list of #defines in a header file for an external library. These #defines represent error codes returned from functions. I want to write a conversion function that can take as an input an error code and return as an output a string literal representing the actual #define name. As an example, if I have #define NO_ERROR 0 #define ONE_KIND_OF_ERROR 1 #define ANOTHER_KIND_OF_ERROR 2 I would like a function to be able to called like int errorCode = doSomeLibraryFunction(); if (errorCode) writeToLog(convertToString(errorCode)); And have convertToString() be able to auto-convert that error code without being a giant switch-case looking like const char* convertToString(int errorCode) { switch (errorCode) { case NO_ERROR: return "NO_ERROR"; case ONE_KIND_OF_ERROR: return "ONE_KIND_OF_ERROR"; ... ... ... I have a feeling that if this is possible, it would be possible using templates and metaprogramming, but that would only work the error codes were actually a type and not a bunch of processor macros. Thanks

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• Context Menu event with QGraphicsWidget

  - by onurozcelik

  In my application I subclass QGraphicsWidget In paint I am drawing a line with pen width 4. I reimplemented boundingRect() and shape(). But I can't catch context menu event every time I click right mouse button. What is the problem.(Pen Width ? ) //Sample code for boundingRect() and shape() QRectF boundingRect() const { qreal rectLeft = x1 < x2 ? x1 : x2; qreal rectTop = y1 < y2 ? y1 : y2; qreal rectWidth = (x1 - x2) != 0 ? abs(x1-x2) : 4; qreal rectHeight = (y1 - y2) != 0 ? abs(y1 -y2) : 4; return QRectF(rectLeft,rectTop,rectWidth,rectHeigt); } QPainterPath shape() { QPainterPath path; path.addRect(boundingRect()); return path; }

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• Obtaining command line arguments in a QT console app

  - by morpheous

  The following snippet is from a little console app I wrote using the QT framework. Currently, it does not receive the arguments passed at the CLI. Can anyone spot what I may be doing wrong? int main(int argc, char *argv[]) { //Q_INIT_RESOURCE(application); try { QApplication the_app(argc, argv); utility::option_values ov; QStringList cmdline_args = QCoreApplication::arguments(); //attempt to parse arguments here, but cmdline_args is an empty list :( ov.parse_options(cmdline_args); // Code continues ... } } catch (utility::invalid_option&) { return 1; } return 0; } I am debugging using QtCreator 1.3

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• [C] Read line from file without knowing the line length.

  - by ryyst

  Hi, I want to read in a file line by line, without knowing the line length before. Here's what I got so far: int ch = getc(file); int length = 0; char buffer[4095]; while (ch != '\n' && ch != EOF) { ch = getc(file); buffer[length] = ch; length++; } printf("Line length: %d characters.", length); I can now figure out the line length, but only for lines that are shorter than 4095 characters. Is there a better way to do this (I already used fgets() but got told it wasn't the best way)? --Ry

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• Keeping historic of modification in a database.

  - by mada

  Hi, Im a j2ee developper & we are using hibernatne mapping with a postgres databasae. We have to keep track of any changes occurs in the databse , in others words alls previous & current value of any field should be saved & field can be various types (bytea, int, char...) With a simple table it is easy but we a graph of objets things are more difficult So we have , speaking in a UML point of view, a graph of objects to store in the database with every changes & the user. Any idea or pattern how to do that ? Thanks in advance.

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