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LoadLibrary (Compact 2013)

  • Article

3/28/2014

This function maps the specified DLL file into the address space of the calling process.

Syntax

HINSTANCE LoadLibrary(
  LPCTSTR lpLibFileName
);

Parameters

  • lpLibFileName
    [in] Pointer to a null-terminated string that names the DLL file.

    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 path but the file does not exist in the specified directory, the function fails.

    When specifying a path, be sure to use backslashes (\), not forward slashes (/).

    If the string does not specify a path, the function uses a standard search strategy to find the file. For more information, see the Remarks section.

Return Value

A handle to the module indicates success. NULL indicates failure. To get extended error information, call GetLastError.

Remarks

LoadLibrary can be used to doing the following:

  • Map a DLL module and return a handle that can be used in GetProcAddress to get the address of a DLL function. You need to use FreeLibrary on the handle later.
  • Map other executable modules. For example, the function can specify an .exe file to get a handle that can be used in FindResource or LoadResource.

Use the CreateProcess function, not LoadLibrary, to run an .exe file.

Applications should cache the handle returned by LoadLibrary to reduce the need for multiple redundant calls. This is of particular performance value when working with the MUI DLL modules, as the libraries will need to be loaded across multiple resources.

If the module is a DLL not already mapped for the calling process, the system calls the DLL's DllMain function with the DLL_PROCESS_ATTACH value.

In Windows Embedded Compact, a DLL is loaded once, but is then mapped into each process's address space when a process implicitly or explicitly loads the library with the LoadLibrary function.

When Windows Embedded Compact loads a DLL, all path information is ignored when determining if the DLL is already loaded. This means that if a DLL with the same name is currently loaded by any process on the system the search order is ignored, even if the path is absolute. In addition, a module ending with the extension .cpl is treated as if the extension is .dll. For example, if Process A loads \Private\mydll.dll and Process B calls LoadLibrary("\Windows\mydll.dll"), Process B will get \Private\mydll.dll.

It is not safe to call LoadLibrary from 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.

Two different modules cannot have the same file name, even if the extensions are different. These effectively have the same module name. For example, if LoadLibrary is made on Sample.cpl, the OS does not load Sample.cpl, but instead loads Sample.dll again.

A similar limitation exists for modules with the same name but residing in different directories. For example, if LoadLibrary is called on \\Windows\Sample.dll, and then LoadLibrary is called on \\MyDir\Sample.dll, \\Windows\Sample.dll will simply be reloaded.

If no file name extension is specified in the lpLibFileName 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.

A search path to the executable module cannot be specified.

Unless the full path to the module is specified, Windows Embedded Compact searches the following path for the module:

  • The absolute path specified by the lpLibFileName parameter.
  • The .exe launch directory.
  • The Windows directory.
  • ROM DLL files.
  • An OEM-specified search path.

The following registry subkey specifies a search path to use with LoadLibrary and CreateProcess:

HKEY_LOCAL_MACHINE\Loader
   SystemPath=multi_sz:\\path1\\
                       \\path2\\

The path is only searched if the path of the file being looked for is not explicitly specified.

The total length of the SystemPath value must not exceed 260 characters. If it does, the path is ignored.

A change to the SystemPath key does not take effect until a Windows Embedded Compact-based device is reset.

When loading a DLL from a process, the run mode of the DLL depends on the run mode of the process. The following table shows the run mode of the DLL depending on whether the calling process is privileged or normal.

Process (.exe) run mode

Privileged DLL run mode

Normal DLL run mode

Privileged

DLL loads as privileged.

DLL not loaded.

Normal

DLL loads as normal.

DLL loaded as normal.

Requirements

Header

winbase.h

Library

coredll.lib

See Also

Reference

DLL Functions
CreateProcess
DllMain
FreeLibrary
GetProcAddress

Other Resources

FindResource
LoadResource
MODULES Section
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