Question

Is there an equivalent of the following on Windows?

#include <dlfcn.h>
#include <stdio.h>

void main_greeting(void)
{
    printf("%s\n", "hello world");
}

void lib_func(void)
{
    void (*greeting)(void) = dlsym(RTLD_MAIN_ONLY, "main_greeting");

    greeting ? greeting() : printf("%s\n", dlerror());
}

int main(void)
{
    lib_func();

    return 0;
}

This is a short snippet, the real purpose is to call a function know to exist at a main process (main_greeting), from inside a function (lib_func) from a dynamic loaded library. The main process is not modifiable, and so cannot be rewritten to pass callbacks.

Answer 1

On Windows, executables and DLLs are of the same format (PE nowadays), so an executable can export functions too. GetProcAddress(GetModuleHandle(NULL),TEXT("main_greeting")) will do what you want if the function is exported from the executable. It’s done by -Wl,-export-all-symbols for mingw GCC.

I believe there is no equivalent option for Microsoft’s linker, so if you use their toolchain, you have to:

• export every function with __declspec(dllexport) in source files,
• or write a module definition file listing every exported function, passing it to linker,
• or generate module definition file automatically.