How Do I Import and Use Functions from DLLs in C ?

Importing Functions from DLLs: A Comprehensive Guide

Loading Dynamic Link Libraries (DLLs) allows your C programs to utilize functionality from external shared libraries. To access functions within a DLL, however, requires a different approach than importing functions from header files.

Loading the DLL with LoadLibrary

The LoadLibrary function loads a DLL into the current process's memory. This process does not automatically import the functions defined in the DLL.

Retrieving the Function Address with GetProcAddress

Once the DLL is loaded, you need to obtain the addresses of the functions you want to use. This is done using the GetProcAddress function.

#include <windows.h>

typedef int (__stdcall *f_funci)();  // Define function pointer type

int main() {
  HINSTANCE hGetProcIDDLL = LoadLibrary("...")

  // Retrieve function address
  f_funci funci = (f_funci)GetProcAddress(hGetProcIDDLL, "funci");
}

In the code snippet above, we define a function pointer type called f_funci that represents the function we want to import. The GetProcAddress function returns the address of the function within the DLL.

Exporting Functions from DLLs

To ensure the proper exporting of functions from a DLL, use the __declspec(dllexport) and __stdcall attributes.

int __declspec(dllexport) __stdcall funci() {
   // ...
}

The __declspec(dllexport) attribute indicates that the function should be exported from the DLL, and the __stdcall attribute specifies the calling convention used by the DLL.

Releasing the DLL Handle

After using the functions imported from the DLL, it's good practice to release the handle to the library. This is accomplished using the FreeLibrary function.

FreeLibrary(hGetProcIDDLL);

By following these steps, you can dynamically load DLLs and access their functions in C . This technique empowers you to extend the capabilities of your programs by utilizing reusable modules without the need for static linking or recompilation.

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