LoadLibraryA function (libloaderapi.h)
Loads the specified module into the address space of the calling process. The specified module may cause other modules to be loaded.
For additional load options, use the LoadLibraryEx function.
Syntax
HMODULE LoadLibraryA(
[in] LPCSTR lpLibFileName
);
Parameters
[in] lpLibFileName
The name of the module. This can be either a library module (a .dll file) or an executable
module (an .exe file).
If the specified module is an executable module, static imports are not loaded;
instead, the module is loaded as if by
LoadLibraryEx
with the DONT_RESOLVE_DLL_REFERENCES flag.
The name specified is the file name of the module and is not related to the name stored in the library module itself, as specified by the LIBRARY keyword in the module-definition (.def) file.
If the string specifies a full path, the function searches only that path for the module.
If the string specifies a relative path or a module name without a path, the function uses a standard search strategy to find the module; for more information, see the Remarks.
If the function cannot find the module, the function fails. When specifying a path, be sure to use backslashes (\), not forward slashes (/). For more information about paths, see Naming a File or Directory.
If the string specifies a module name without a path and the file name extension is omitted, the function appends the default library extension ".DLL" to the module name. To prevent the function from appending ".DLL" to the module name, include a trailing point character (.) in the module name string.
Return value
If the function succeeds, the return value is a handle to the module.
If the function fails, the return value is NULL. To get extended error information, call GetLastError.
Remarks
To enable or disable error messages displayed by the loader during DLL loads, use the SetErrorMode function.
LoadLibrary can be used to load a library module into the address space of the process and return a handle that can be used in GetProcAddress to get the address of a DLL function. LoadLibrary can also be used to load other executable modules. For example, the function can specify an .exe file to get a handle that can be used in FindResource or LoadResource. However, do not use LoadLibrary to run an .exe file. Instead, use the CreateProcess function.
If the specified module is a DLL that is not already loaded for the calling process, the system calls the DLL's DllMain function with the DLL_PROCESS_ATTACH value. If DllMain returns TRUE, LoadLibrary returns a handle to the module. If DllMain returns FALSE, the system unloads the DLL from the process address space and LoadLibrary returns NULL. It is not safe to call LoadLibrary from DllMain. For more information, see the Remarks section in DllMain.
Module handles are not global or inheritable. A call to LoadLibrary by one process does not produce a handle that another process can use — for example, in calling GetProcAddress. The other process must make its own call to LoadLibrary for the module before calling GetProcAddress.
If lpFileName does not include a path and there is more than one loaded module with the same base name and extension, the function returns a handle to the module that was loaded first.
If no file name extension is specified in the lpFileName parameter, the default library extension .dll is appended. However, the file name string can include a trailing point character (.) to indicate that the module name has no extension. When no path is specified, the function searches for loaded modules whose base name matches the base name of the module to be loaded. If the name matches, the load succeeds. Otherwise, the function searches for the file.
The first directory searched is the directory containing the image file used to create the calling process (for more information, see the CreateProcess function). Doing this allows private dynamic-link library (DLL) files associated with a process to be found without adding the process's installed directory to the PATH environment variable. If a relative path is specified, the entire relative path is appended to every token in the DLL search path list. To load a module from a relative path without searching any other path, use GetFullPathName to get a nonrelative path and call LoadLibrary with the nonrelative path. For more information on the DLL search order, see Dynamic-Link Library Search Order.
The search path can be altered using the SetDllDirectory function. This solution is recommended instead of using SetCurrentDirectory or hard-coding the full path to the DLL.
If a path is specified and there is a redirection file for the application, the function searches for the module in the application's directory. If the module exists in the application's directory, LoadLibrary ignores the specified path and loads the module from the application's directory. If the module does not exist in the application's directory, LoadLibrary loads the module from the specified directory. For more information, see Dynamic Link Library Redirection.
If you call LoadLibrary with the name of an assembly without a path specification and the assembly is listed in the system compatible manifest, the call is automatically redirected to the side-by-side assembly.
The system maintains a per-process reference count on all loaded modules. Calling LoadLibrary increments the reference count. Calling the FreeLibrary or FreeLibraryAndExitThread function decrements the reference count. The system unloads a module when its reference count reaches zero or when the process terminates (regardless of the reference count).
Windows Server 2003 and Windows XP: The Visual C++ compiler supports a syntax that enables you to declare thread-local variables: _declspec(thread). If you use this syntax in a DLL, you will not be able to load the DLL explicitly using LoadLibrary on versions of Windows prior to Windows Vista. If your DLL will be loaded explicitly, you must use the thread local storage functions instead of _declspec(thread). For an example, see Using Thread Local Storage in a Dynamic Link Library.
Security Remarks
Do not use the SearchPath function to retrieve a path to a DLL for a subsequent LoadLibrary call. The SearchPath function uses a different search order than LoadLibrary and it does not use safe process search mode unless this is explicitly enabled by calling SetSearchPathMode with BASE_SEARCH_PATH_ENABLE_SAFE_SEARCHMODE. Therefore, SearchPath is likely to first search the user’s current working directory for the specified DLL. If an attacker has copied a malicious version of a DLL into the current working directory, the path retrieved by SearchPath will point to the malicious DLL, which LoadLibrary will then load.Do not make assumptions about the operating system version based on a LoadLibrary call that searches for a DLL. If the application is running in an environment where the DLL is legitimately not present but a malicious version of the DLL is in the search path, the malicious version of the DLL may be loaded. Instead, use the recommended techniques described in Getting the System Version.
Examples
For an example, see Using Run-Time Dynamic Linking.
Note
The libloaderapi.h header defines LoadLibrary as an alias that automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that is not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | Windows XP [desktop apps only] |
| Minimum supported server | Windows Server 2003 [desktop apps only] |
| Target Platform | Windows |
| Header | libloaderapi.h (include Windows.h) |
| Library | Kernel32.lib |
| DLL | Kernel32.dll |