DuplicateHandle

The DuplicateHandle function duplicates an object handle. The duplicate handle refers to the same object as the original handle. Therefore, any changes to the object are reflected through both handles. For example, the current file mark for a file handle is always the same for both handles.

BOOL DuplicateHandle(
  HANDLE hSourceProcessHandle,  // handle to source process
  HANDLE hSourceHandle,         // handle to duplicate
  HANDLE hTargetProcessHandle,  // handle to target process
  LPHANDLE lpTargetHandle,      // duplicate handle
  DWORD dwDesiredAccess,        // requested access
  BOOL bInheritHandle,          // handle inheritance option
  DWORD dwOptions               // optional actions
);

Parameters

hSourceProcessHandle

[in] Handle to the process with the handle to duplicate.

Windows NT/2000: The handle must have PROCESS_DUP_HANDLE access. For more information, see Process Security and Access Rights.

hSourceHandle

[in] Handle to duplicate. This is an open object handle that is valid in the context of the source process. For a list of objects whose handles can be duplicated, see the following Remarks section.

hTargetProcessHandle

[in] Handle to the process that is to receive the duplicated handle. The handle must have PROCESS_DUP_HANDLE access.

lpTargetHandle

[out] Pointer to a variable that receives the value of the duplicate handle. This handle value is valid in the context of the target process.

If lpTargetHandle is NULL, the function duplicates the handle, but does not return the duplicate handle value to the caller. This behavior exists only for backward compatibility with previous versions of this function. You should not use this feature, as you will lose system resources until the target process terminates.

dwDesiredAccess

[in] Specifies the access requested for the new handle. This parameter is ignored if the dwOptions parameter specifies the DUPLICATE_SAME_ACCESS flag. Otherwise, the flags that can be specified depend on the type of object whose handle is being duplicated. For the flags that can be specified for each object type, see the following Remarks section. Note that the new handle can have more access than the original handle.

bInheritHandle

[in] Indicates whether the handle is inheritable. If TRUE, the duplicate handle can be inherited by new processes created by the target process. If FALSE, the new handle cannot be inherited.

dwOptions

[in] Specifies optional actions. This parameter can be zero, or any combination of the following values.

Value	Meaning
DUPLICATE_CLOSE_SOURCE	Closes the source handle. This occurs regardless of any error status returned.
DUPLICATE_SAME_ACCESS	Ignores the dwDesiredAccess parameter. The duplicate handle has the same access as the source handle.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

DuplicateHandle can be called by either the source process or the target process. It can also be invoked where the source and target process are the same. For example, a process can use DuplicateHandle to create a noninheritable duplicate of an inheritable handle, or a handle with different access than the original handle.

The duplicating process uses the GetCurrentProcess function to get a handle of itself. To get the other process handle, it may be necessary to use some form of interprocess communication (for example, named pipe or shared memory) to communicate the process identifier to the duplicating process. This identifier is then used in the OpenProcess function to open a handle.

If the process that calls DuplicateHandle is not the target process, the duplicating process must use interprocess communication to pass the value of the duplicate handle to the target process.

DuplicateHandle can duplicate handles to the following types of objects.

Note that DuplicateHandle should not be used to duplicate handles to I/O completion ports. In this case, no error is returned, but the duplicate handle cannot be used.

In addition to STANDARD_RIGHTS_REQUIRED, the following access flags can be specified in the dwDesiredAccess parameter for the different object types. Note that the new handle can have more access than the original handle. However, in some cases DuplicateHandle cannot create a duplicate handle with more access permission than the original handle. For example, a file handle created with GENERIC_READ access cannot be duplicated so that it has both GENERIC_READ and GENERIC_WRITE access.

Any combination of the following access flags is valid for handles to communications devices, console input, console screen buffers, files, and pipes.

Any combination of the following access flags is valid for file-mapping objects.

Any combination of the following flags is valid for mutex objects.

Any combination of the following access flags is valid for semaphore objects.

Any combination of the following access flags is valid for event objects.

Any combination of the following access flags is valid for handles to registry keys.

Any combination of the following access flags is valid for process objects.

Any combination of the following access flags is valid for thread objects.

Requirements

  Windows NT/2000: Requires Windows NT 3.1 or later.
  Windows 95/98: Requires Windows 95 or later.
  Header: Declared in Winbase.h; include Windows.h.
  Library: Use Kernel32.lib.

See Also

Handles and Objects Overview, Handle and Object Functions, CloseHandle