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CreatePipe function

Creates an anonymous pipe, and returns handles to the read and write ends of the pipe.

Syntax


BOOL WINAPI CreatePipe(
  _Out_     PHANDLE hReadPipe,
  _Out_     PHANDLE hWritePipe,
  _In_opt_  LPSECURITY_ATTRIBUTES lpPipeAttributes,
  _In_      DWORD nSize
);

Parameters

hReadPipe [out]

A pointer to a variable that receives the read handle for the pipe.

hWritePipe [out]

A pointer to a variable that receives the write handle for the pipe.

lpPipeAttributes [in, optional]

A pointer to a SECURITY_ATTRIBUTES structure that determines whether the returned handle can be inherited by child processes. If lpPipeAttributes is NULL, the handle cannot be inherited.

The lpSecurityDescriptor member of the structure specifies a security descriptor for the new pipe. If lpPipeAttributes is NULL, the pipe gets a default security descriptor. The ACLs in the default security descriptor for a pipe come from the primary or impersonation token of the creator.

nSize [in]

The size of the buffer for the pipe, in bytes. The size is only a suggestion; the system uses the value to calculate an appropriate buffering mechanism. If this parameter is zero, the system uses the default buffer size.

Return value

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

CreatePipe creates the pipe, assigning the specified pipe size to the storage buffer. CreatePipe also creates handles that the process uses to read from and write to the buffer in subsequent calls to the ReadFile and WriteFile functions.

To read from the pipe, a process uses the read handle in a call to the ReadFile function. ReadFile returns when one of the following is true: a write operation completes on the write end of the pipe, the number of bytes requested has been read, or an error occurs.

When a process uses WriteFile to write to an anonymous pipe, the write operation is not completed until all bytes are written. If the pipe buffer is full before all bytes are written, WriteFile does not return until another process or thread uses ReadFile to make more buffer space available.

Anonymous pipes are implemented using a named pipe with a unique name. Therefore, you can often pass a handle to an anonymous pipe to a function that requires a handle to a named pipe.

If CreatePipe fails, the contents of the output parameters are indeterminate. No assumptions should be made about their contents in this event.

To free resources used by a pipe, the application should always close handles when they are no longer needed, which is accomplished either by calling the CloseHandle function or when the process associated with the instance handles ends. Note that an instance of a pipe may have more than one handle associated with it. An instance of a pipe is always deleted when the last handle to the instance of the named pipe is closed.

Examples

For an example, see Creating a Child Process with Redirected Input and Output.

Requirements

Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]

Header

Winbase.h (include Windows.h)

Library

Kernel32.lib

DLL

Kernel32.dll

See also

Pipe Functions
Pipes Overview
ReadFile
SECURITY_ATTRIBUTES
WriteFile

 

 

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