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  • Flexible array members in C - bad?

    - by Lionel
    I recently read that using flexible array members in C was poor software engineering practice. However, that statement was not backed by any argument. Is this an accepted fact? (Flexible array members are a C feature introduced in C99 whereby one can declare the last element to be an array of unspecified size. For example: ) struct header { size_t len; unsigned char data[]; };

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  • Detect if class has overloaded function fails on Comeau compiler

    - by Frank
    Hi Everyone, I'm trying to use SFINAE to detect if a class has an overloaded member function that takes a certain type. The code I have seems to work correctly in Visual Studio and GCC, but does not compile using the Comeau online compiler. Here is the code I'm using: #include <stdio.h> //Comeau doesnt' have boost, so define our own enable_if_c template<bool value> struct enable_if_c { typedef void type; }; template<> struct enable_if_c< false > {}; //Class that has the overloaded member function class TestClass { public: void Func(float value) { printf( "%f\n", value ); } void Func(int value) { printf( "%i\n", value ); } }; //Struct to detect if TestClass has an overloaded member function for type T template<typename T> struct HasFunc { template<typename U, void (TestClass::*)( U )> struct SFINAE {}; template<typename U> static char Test(SFINAE<U, &TestClass::Func>*); template<typename U> static int Test(...); static const bool Has = sizeof(Test<T>(0)) == sizeof(char); }; //Use enable_if_c to only allow the function call if TestClass has a valid overload for T template<typename T> typename enable_if_c<HasFunc<T>::Has>::type CallFunc(TestClass &test, T value) { test.Func( value ); } int main() { float value1 = 0.0f; int value2 = 0; TestClass testClass; CallFunc( testClass, value1 ); //Should call TestClass::Func( float ) CallFunc( testClass, value2 ); //Should call TestClass::Func( int ) } The error message is: no instance of function template "CallFunc" matches the argument list. It seems that HasFunc::Has is false for int and float when it should be true. Is this a bug in the Comeau compiler? Am I doing something that's not standard? And if so, what do I need to do to fix it?

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  • template; operator (int)

    - by Oops
    Hi, regarding my Point struct already mentioned here: http://stackoverflow.com/questions/2794369/template-class-ctor-against-function-new-c-standard is there a chance to replace the function toint() with a cast-operator (int)? namespace point { template < unsigned int dims, typename T > struct Point { T X[ dims ]; //umm??? template < typename U > Point< dims, U > operator U() const { Point< dims, U > ret; std::copy( X, X + dims, ret.X ); return ret; } //umm??? Point< dims, int > operator int() const { Point<dims, int> ret; std::copy( X, X + dims, ret.X ); return ret; } //OK Point<dims, int> toint() { Point<dims, int> ret; std::copy( X, X + dims, ret.X ); return ret; } }; //struct Point template < typename T > Point< 2, T > Create( T X0, T X1 ) { Point< 2, T > ret; ret.X[ 0 ] = X0; ret.X[ 1 ] = X1; return ret; } }; //namespace point int main(void) { using namespace point; Point< 2, double > p2d = point::Create( 12.3, 34.5 ); Point< 2, int > p2i = (int)p2d; //äähhm??? std::cout << p2d.str() << std::endl; char c; std::cin >> c; return 0; } I think the problem is here that C++ cannot distinguish between different return types? many thanks in advance. regards Oops

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  • Do I need to cast the result of strtol to int?

    - by Kristo
    The following code does not give a warning with g++ 4.1.1 and -Wall. int octalStrToInt(const std::string& s) { return strtol(s.c_str(), 0, 8); } I was expecting a warning because strtol returns a long int but my function is only returning a plain int. Might other compilers emit a warning here? Should I cast the return value to int in this case as a good practice?

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  • Comparing the values of two nsstrings

    - by user1776234
    So I have been trying to compare two NSStrings in xcode. However, it is not working. What am I doing wrong? NSString Prog are characters that are xml parsed from mysql char *cStr = "YES"; NSString *str3 = [NSString stringWithUTF8String:cStr]; if ([str3 isEqualToString:prog]) { [switch1 setOn:YES animated:YES]; } else { [switch1 setOn:NO animated:YES]; }

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  • sed as grep + ignore # and match

    - by yael
    I have the following file example more somefile param=a b c d e f g z x w # param=a b c d e f g z x w I need to create with sed the following (should be one line if possible): Ignore # char in the beginning of line Match first the param string Second match the "a b c d e f g z x w" (like grep -w) and give exit status if success Something like .... sed "/^ *#/b; /\<param\>/" ....

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  • What happens when I throw an exception?

    - by helloWorld
    I have some technical questions. In this function: string report() const { if(list.begin() == list.end()){ throw "not good"; } //do something } If I throw the exception what is going on with the program? Will my function terminate or will it run further? If it terminates, what value will it return?

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  • Is this a correct syntax (c code found on wikipedia)?

    - by m4design
    I just found this code on wikipedia. Link: http://en.wikipedia.org/wiki/Sizeof#Use The code: /* the following code illustrates the use of sizeof * with variables and expressions (no parentheses needed), * and with type names (parentheses needed) */ char c; printf("%zu,%zu", sizeof c, sizeof(int)); It states that: "The z prefix should be used to print it, because the actual size can differ on each architecture." I tried it on my compiler, but it gives the following result: 'zu,zu'

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  • Access Voilation in std::pair

    - by sameer karjatkar
    I have an application which is trying to populate a pair . Out of no where the application crashes . The Windbg analysis on the crash dump suggest PRIMARY_PROBLEM_CLASS: INVALID_POINTER_READ DEFAULT_BUCKET_ID: INVALID_POINTER_READ STACK_TEXT: 0389f1dc EPFilter32!std::vector,std::allocator ::size+0xc INVALID_POINTER_READ_c0000005_Test.DLL!std::vector_std::pair_unsigned_int, unsigned_int_,std::allocator_std::pair_unsigned_int,unsigned_int___::size Following is the statement in the code where it fails const branch_info& b1 = en1.m_branches[i1]; where branch_info is std::pair and the en1.m_branches[i1] fetches me a pair value

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  • C++ How fast is passing around objects?

    - by wndsr
    Assuming we are running a compiled C++ binary: Is passing around an int (e.g. function to function, or writing it into variables) slower than passing around structs/class objects like the following? class myClass { int a; int b; char c; vector d; string e; }

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  • Better alternative for PipedReader/PipedWriter?

    - by Esko Luontola
    I need to have a buffered char stream, into which I write in one thread and from which I read in another thread. Right now I'm using PipedReader and PipedWriter for it, but those classes cause a performance problem: PipedReader does a wait(1000) when its internal buffer is empty, which causes my application to lag visibly. Would there be some library which does the same thing as PipedReader/PipedWriter, but with better performance? Or will I have to implement my own wheels?

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  • C++: Chr() and unichr() equivalent?

    - by alex
    I could have sworn I used a chr() function 40 minutes ago but can't find the file. I know it can go up to 256 so I use this: std::string chars = ""; chars += (char) 42; //etc So that's alright, but I really want to access unicode characters. Can I do (w_char) 512? Or maybe something just like the unichr() function in python, I just can't find a way to access any of those characters.

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  • How to interpret binary data as an integer?

    - by StackedCrooked
    The codebase at work contains some code that looks roughly like this: #define DATA_LENGTH 64 u_int32 SmartKey::SerialNumber() { unsigned char data[DATA_LENGTH]; // ... initialized data buffer return *(u_int32*)data; } This code works correctly, but GCC gives the following warning: warning: dereferencing pointer ‘serialNumber’ does break strict-aliasing rules Can someone explain this warning? Is this code potentially dangerous? How can it be improved?

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  • strict string to int[long]

    - by baskin
    Do we have a standard way of converting a char* to int (or long) in a strict way, i.e. we should get proper result only if all characters are digits and can fit in an int (or long) -- some way by using strtol etc.. ? Thus "sbc45", "4590k", " 56", "56 ", should be all invalid using that function.

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