c99

问题 I have this code which works: #include <stdio.h> #define A(x) x B #define B(x) C(x, #define C(x,y) y x) int main( void ) { printf( A("1") ("2") "3" ); } It prints 132 (the point of the A macro is to swap the thing which follows its parameters in brackets with everything after that until another closing bracket) But if I use that within another macro: #define Z(x) x printf( Z( A("1") ("2") "3" ) ); I get the compile error "Unterminated function-like macro invocation". I realise that this

问题 After reading about VA_NARG I tried to implement function overloading depending on number of arguments in C using macros. Now the problem is: void hello1(char *s) { ... } void hello2(char *s, char *t) { ... } // PP_NARG(...) macro returns number of arguments :ref to link above // does not work #define hello(...) hello ## PP_NARG(__VA_ARGS__) int main(void) { hello("hi"); // call hello1("hi"); hello("foo","bar"); // call hello2("foo","bar"); return 0; } I've read this from C-faq. But still

问题 I have a header file that is going to contain a large amount (30+) of inline functions. Rather than having the reader scroll or search for the definition (implementation) of the inline function, I would like to have a forward declaration section that states the function declaration with comments describing the function. This section would allow the reader to find out how to use a function or to look for a function without having to scroll down to the implementation. Also, I would like the

问题 If I've got a pointer to some heap allocated space that represents a typical row-major two dimensional array, is it safe to cast this pointer to an equivalent pointer to a VLA for convenient sub-scripting? Example: // // Assuming 'm' was allocated and initialized something like: // // int *matrix = malloc(sizeof(*matrix) * rows * cols); // // for (int r = 0; r < rows; r++) { // for (int c = 0; c < cols; c++) { // matrix[r * cols + c] = some_value; // } // } // // Is it safe for this function

问题 GCC complains if I do this: #define M(obj,met, ..., contents) obj##_##met(const void * self, __VA_ARGS__) { \ contents \ } Giving me these 2 reasons: error: missing ')' in macro parameter list warning: __VA_ARGS__ can only appear in the expansion of a C99 variadic macro Apparently, C99 - style variadic macros expect the closing parenthesis immediately after the ellipsis, effectively demanding that the variadic list be the last arguments of the macro. I need it to be in the middle to produce

问题 I just read: C Wikipedia entry. As far as I know there are 3 different versions of C that are widely used: C89, C99 and C11. My question concerns the compatibility of source code of different versions. Suppose I am going to write a program (in C11 since it is the latest version) and import a library written in C89. Are these two versions going to work together properly when compiling all files according to the C11 specification? Question 1 : Are the newer versions of C i.e. C99, C11 supersets

问题 What gcc options shall I use to enforce ANSI C (C99) warnings/errors? gcc (GCC) 3.4.2 (mingw-special) I'm using: gcc -pedantic -ansi -std=c99 is this correct? 回答1: The -ansi flag is synonymous with the -std=c89 flag. Just using -std=c99 with -pedantic should be sufficient. When in doubt, you can always refer to the GCC documentation. As of GCC 3.4.2, the chapter to read is 2 - Language Standards Supported by GCC. 回答2: This is an old question but I just wanted to add some extra points. Firstly

问题 Thankfully, the complex type modifier was introduced into C99 standard. What I don't understand is why it was decided to omit support for fixed point arithmetic (specifically, support fractional types like 1.15 {signed} or 0.32 {unsigned}) where these types are so fundamental to DSP programming? Does GCC support these through an extension? 回答1: It's been discussed/proposed (e.g., in N938, N953) but those papers have only proposed it as extensions, not additions to the main standard. Those

问题 Trying some code I realized that the following code compiles: struct { int x, y; } foo(void) { } It seems as if we are defining a function named foo which returns an anonymous struct . Now, my question is: Does it only happen to compile with my compiler or is this legal C(99)? If so, what is the correct syntax for a return statement and how can I correctly assign the returned value to a variable? 回答1: The struct you're returning is not an anonymous struct. C standard defines an anonymous

问题 I'm programming in C99 and use variable length arrays in one portion of my code. I know in C89 zero-length arrays are not allowed, but I'm unsure of C99 and variable length arrays. In short, is the following well defined behavior? int main() { int i = 0; char array[i]; return 0; } 回答1: No, zero-length arrays are explicitly prohibited by C language, even if they are created as VLA through a run-time size value (as in your code sample). 6.7.5.2 Array declarators ... 5 If the size is an