Pre/Post-main Function Call Implementation in C

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:

#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

#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:

/*
 * 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;
}

* 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

void before()

{

printf("before main\n");

}

void after()

{

printf("after main\n");

}

int main()

{

printf("in main\n");

return 0;

}

Output from msvc/gcc:

before main
in main
after main

before main

in main

after main

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