In C++, pre/post-main function call can be implemented using a global class instance. Its constructor and destructor are invoked automatically before and after the main function. But in C, no such mechanism. Actually, there’s a glib implementation that can help. You may want to read my previous post about CRT sections of MSVC. I just copy the code and do some renaming:
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#include <stdlib.h> #if defined (_MSC_VER) #if (_MSC_VER >= 1500) /* Visual Studio 2008 and later have __pragma */ #define HAS_CONSTRUCTORS #define DEFINE_CONSTRUCTOR(_func) \ static void _func(void); \ static int _func ## _wrapper(void) { _func(); return 0; } \ __pragma(section(".CRT$XCU",read)) \ __declspec(allocate(".CRT$XCU")) static int (* _array ## _func)(void) = _func ## _wrapper; #define DEFINE_DESTRUCTOR(_func) \ static void _func(void); \ static int _func ## _constructor(void) { atexit (_func); return 0; } \ __pragma(section(".CRT$XCU",read)) \ __declspec(allocate(".CRT$XCU")) static int (* _array ## _func)(void) = _func ## _constructor; #elif (_MSC_VER >= 1400) /* Visual Studio 2005 */ #define HAS_CONSTRUCTORS #pragma section(".CRT$XCU",read) #define DEFINE_CONSTRUCTOR(_func) \ static void _func(void); \ static int _func ## _wrapper(void) { _func(); return 0; } \ __declspec(allocate(".CRT$XCU")) static int (* _array ## _func)(void) = _func ## _wrapper; #define DEFINE_DESTRUCTOR(_func) \ static void _func(void); \ static int _func ## _constructor(void) { atexit (_func); return 0; } \ __declspec(allocate(".CRT$XCU")) static int (* _array ## _func)(void) = _func ## _constructor; #else /* Visual Studio 2003 and early versions should use #pragma code_seg() to define pre/post-main functions. */ #error Pre/Post-main function not supported on your version of Visual Studio. #endif #elif (__GNUC__ > 2) || (__GNUC__ == 2 && __GNUC_MINOR__ >= 7) #define HAS_CONSTRUCTORS #define DEFINE_CONSTRUCTOR(_func) static void __attribute__((constructor)) _func (void); #define DEFINE_DESTRUCTOR(_func) static void __attribute__((destructor)) _func (void); #else /* not supported */ #endif |
One limitation in glib code is the lack of support for VS2003 and early versions. #pragma code_seg() is used to implement the same function:
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/* * cl ctor.c * gcc ctor.c -o ctor */ #include "ctor.h" #include <stdio.h> #ifdef HAS_CONSTRUCTORS DEFINE_CONSTRUCTOR(before) DEFINE_DESTRUCTOR(after) #else #ifdef _MSC_VER static void before(void); static void after(void); #pragma data_seg(".CRT$XCU") static void (*msc_ctor)(void) = before; #pragma data_seg(".CRT$XPU") static void (*msc_dtor)(void) = after; #pragma data_seg() #endif #endif void before() { printf("before main\n"); } void after() { printf("after main\n"); } int main() { printf("in main\n"); return 0; } |
Output from msvc/gcc:
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before main in main after main |