GetProcAddress

GetProcAddress is a Windows API function that retrieves the address of an exported function or variable from a specified dynamic-link library (DLL) module. It supports dynamic or late binding by allowing a program to resolve function addresses at runtime rather than at load time, enabling plugins, optional features, and runtime binding to DLLs.

The function is declared as FARPROC GetProcAddress(HMODULE hModule, LPCSTR lpProcName). The hModule parameter is a handle to a loaded module, obtained via LoadLibrary or GetModuleHandle. The lpProcName parameter specifies the export name as an ANSI string; it can alternatively indicate an ordinal value by passing MAKEINTRESOURCE with an ordinal, in which case the high-order word of lpProcName is zero and the low-order word is the ordinal. The return value is a pointer to the requested function or variable, which should be cast to the appropriate function pointer type by the caller. If the function or ordinal is not found, GetProcAddress returns NULL and the caller may call GetLastError to obtain more information, though some implementations do not reliably set an error.

Usage considerations include ensuring the DLL remains loaded for the duration of the call and any subsequent use of the returned pointer, and acknowledging that exported names are case-sensitive in most PE implementations. GetProcAddress is commonly used for implementing optional features, plugin architectures, and compatibility shims, as well as for calling functions whose availability may vary across Windows versions or configurations. It is used in conjunction with LoadLibrary or GetModuleHandle and FreeLibrary as part of dynamic linking practices. See also LoadLibrary, GetModuleHandle, and FreeLibrary.