loadlibrary

LoadLibrary is a Windows API function used to load a dynamic-link library (DLL) into the address space of the calling process and obtain a handle to the loaded module. In C and C++, the functions are declared as HMODULE LoadLibraryA(LPCSTR lpFileName) and HMODULE LoadLibraryW(LPCWSTR lpFileName); the generic LoadLibrary maps to LoadLibraryW in Unicode builds.

When successful, LoadLibrary loads the specified DLL into memory, increments the library’s reference count, and loads the library’s dependencies as needed. The function returns a module handle that can be used with GetProcAddress to locate exported functions. The loaded module remains in the process until FreeLibrary is called and its reference count drops to zero, or the process terminates.

If loading fails, the function returns NULL and extended error information can be retrieved with GetLastError. Common errors include ERROR_MOD_NOT_FOUND, ERROR_DLL_NOT_FOUND, and ERROR_BAD_EXE_FORMAT. The search behavior depends on whether the file name includes a path; a fully qualified path loads from that location, while a relative name uses the system DLL search path, which typically includes the directory of the calling process, system directories, Windows directory, current directory, and PATH, subject to OS version and security settings.

Security considerations arise from the potential for DLL hijacking if untrusted or relative paths are used. Best practices include using fully qualified paths, or controls over the search path via APIs such as SetDefaultDllDirectories and AddDllDirectory, to restrict where libraries may be loaded from.

Related functions include LoadLibraryEx (which provides additional flags to alter search behavior), FreeLibrary (to unload), GetProcAddress (to obtain function pointers), and GetModuleHandle (to obtain a handle to an already loaded module). LoadLibrary is a core mechanism for dynamic binding and plugin architectures on Windows.