How to import a DLL function in C?

Question

I was given a DLL that I'm trying to use. The DLL contains the function "send". this is what I did:

#include <stdio.h>
#include <Windows.h>

int main(int argc, char * argv[])
{
    HMODULE libHandle;

    if ((libHandle = LoadLibrary(TEXT("SendSMS.dll"))) == NULL)
    {
        printf("load failed\n");
        return 1;
    }
    if (GetProcAddress(libHandle, "send") == NULL)
    {
        printf("GetProcAddress failed\n");
        printf("%d\n", GetLastError());
        return 1;
    }
    return 0;
}

GetProcAddress returns NULL, and the last error value is 127. (procedure was not found)

What am I doing wrong?

Answer 1

Code look more or less good, so probably something is wrong with *.dll. Please download Dependency Walker application and check what kind of functions are exported by this library.

Answer 2

Probably the DLL doesn't export such a function.

This is usually caused by the "decorations" the compiler adds to the function name. For instance "send" may actually be seen as:

• _send
• _send@4
• ?send@@ABRACADABRA

To resolve this that's what you should do:

1. Use the "depends" utility (depends32.exe, shipped with MSVC) to view what your DLL actually exports.
2. If you're the author of the DLL - you may force the export name to be what you want, by using "def" file (for linker)

Answer 3

I noticed that you're using TEXT on LoadLibrary, but not on GetProcAddress. If GetProcAddress is misinterpreting your string, it could be looking for the wrong function.

Answer 4

If you running 64bit environment and "sendsms.dll" is compiled as 32bit loadlibrary does not work. You need to compile your project as 32bit to load dlls.