How can I compose translation units in C? [duplicate] - c++

Question

I was wondering if it's possible to use C constructors in VC just as it is possible to use them in GCC.
The gcc way is quite straight using the __attribute__ keyword, unfortunately VC doesn't seem to even know this keyword, as I'm not a Win32 programmer I wonder if there's some sort of equivalent keyword for such things.
Just to note - this is a C program, not a C++ or C# even, (as 'twas quite easy to do that in those languages)

Answer 1

Below C code demonstrates how to define a void(void) function to be called at program/library load time, before main executes.
For MSVC, this places a pointer to the function in the user initializer section (.CRT$XCU), basically the same thing the compiler does for the constructor calls for static C++ objects. For GCC, uses a constructor attribute.
// Initializer/finalizer sample for MSVC and GCC/Clang.
// 2010-2016 Joe Lowe. Released into the public domain.
#include <stdio.h>
#include <stdlib.h>
#ifdef __cplusplus
#define INITIALIZER(f) \
static void f(void); \
struct f##_t_ { f##_t_(void) { f(); } }; static f##_t_ f##_; \
static void f(void)
#elif defined(_MSC_VER)
#pragma section(".CRT$XCU",read)
#define INITIALIZER2_(f,p) \
static void f(void); \
__declspec(allocate(".CRT$XCU")) void (*f##_)(void) = f; \
__pragma(comment(linker,"/include:" p #f "_")) \
static void f(void)
#ifdef _WIN64
#define INITIALIZER(f) INITIALIZER2_(f,"")
#else
#define INITIALIZER(f) INITIALIZER2_(f,"_")
#endif
#else
#define INITIALIZER(f) \
static void f(void) __attribute__((constructor)); \
static void f(void)
#endif
static void finalize(void)
{
printf( "finalize\n");
}
INITIALIZER( initialize)
{
printf( "initialize\n");
atexit( finalize);
}
int main( int argc, char** argv)
{
printf( "main\n");
return 0;
}

Answer 2

You are probably interested in DllMain.

Answer 3

I don't think there's a way to avoid using C++ features with MSVC. (MSVC's C support sucks anyways.)
Untested, but this should at least allow the same code to work in both MSVC and GCC.
#if defined(_MSC_VER)
struct construct { construct(void (*f)(void)) { f(); } };
#define constructor(fn) \
void fn(void); static constructor constructor_##fn(fn)
#elif defined(__GNUC__)
#define constructor(fn)
void fn(void) __attribute__((constructor))
#endif
static constructor(foo);
void foo() {
...
}

Answer 4

I tried the last answer in MSVC like
#ifdef _MSC_VER
#pragma section(".CRT$XCU",read)
#define INITIALIZER2_(f,p) \
static void f(void); \
__declspec(allocate(".CRT$XCU")) void (*f##_)(void) = f; \
__pragma(comment(linker,"/include:" p #f "_")) \
static void f(void)
#ifdef _WIN64
#define INITIALIZER(f) INITIALIZER2_(f,"")
#else
#define INITIALIZER(f) INITIALIZER2_(f,"_")
#endif
#else
#define INITIALIZER(f) \
static void f(void) __attribute__((constructor)); \
static void f(void)
#endif
but INITIALIZER(f) can't appear in 2 different files with the same function name passed to INITIALIZER, the following definition will allow that
#ifdef _MSC_VER
#define INITIALIZER(f) \
static void f();\
static int __f1(){f();return 0;}\
__pragma(data_seg(".CRT$XIU"))\
static int(*__f2) () = __f1;\
__pragma(data_seg())\
static void f()
#else
#define INITIALIZER(f) \
__attribute__((constructor)) static void f()
#endif