Anonymous Pipes Overview - Win32 Programmer's Reference

Custom Search

Anonymous Pipes Overview

A typical use of an anonymous pipe is to create a channel for communication between a parent process and its child process by redirecting the standard input or standard output handles of the child process. To redirect the standard output handle of a child process, the parent process performs the following steps:

Call the GetStdHandle function to get the current standard output handle; save the handle for later use.
Call the CreatePipe function to create an anonymous pipe. This function returns handles to the read and write ends of the pipe.
Call the SetStdHandle function to set its standard output to be the write handle of the pipe.
Call the CreateProcess function to create the child process. The child process inherits the inheritable handles of the parent process. It also inherits the values of the standard handles of its parent process, which it can retrieve using the GetStdHandle function.
Call the CloseHandle function to close the parent's handle to the write end of the pipe. After the child process inherits this handle, the parent process no longer needs its copy of the handle.
Call the ReadFile function to read from the pipe. This operation enables the parent process to read the data written to standard output by the child process.

The child process uses the GetStdHandle function to get its standard output handle, which is actually a handle to the write end of the pipe. The child process then uses the WriteFile function to write its output to the pipe.

Data is written to an anonymous pipe as a stream of bytes. This means that a process reading from a pipe cannot distinguish between the bytes written in separate write operations, unless both reading and writing processes use some protocol that lets the reading process know how many bytes to read. Typically, there is no protocol, so the reading process reads from the pipe until all write handles to the pipe are closed, which causes the ReadFile function to return FALSE. When a child process's standard output is redirected, the child process calls CloseHandle or terminates (which automatically closes the handle). Note that it is important for the parent process to close its handle to the write end of the pipe before trying to read from the pipe. Otherwise, its ReadFile operation cannot return FALSE because there is still an open handle to the write end of the pipe.

The procedure for redirecting standard input is similar to that for redirecting standard output, except that the pipe's read handle is used for the child's standard input. In this case, the parent process must ensure that the child process does not inherit the pipe's write handle. Otherwise, the ReadFile operation of the child process cannot return FALSE because the child process has an open handle to the write end of the pipe.

The parent process typically creates the read and write handles to the pipe so that they can be inherited by a child process. It does this by using CreatePipe, specifying a SECURITY_ATTRIBUTES structure with the bInheritHandle member set to TRUE. When a child's standard input is redirected, the child process should not inherit the pipe's write handle. The parent process prevents inheritance by using the DuplicateHandle function to create a noninheritable duplicate of the handle and then using CloseHandle to close the inheritable handle.

For an example program that uses anonymous pipes to redirect the standard handles of a child process, see Processes and Threads.

Last news from Greatis Software

    Nostalgia .Net     .Net is powerful, but not all-powerful, so sometimes we need to use Win32 API for our .Net applications. It's simple enough with Platform Invoke if you have Win32 skill, but we do not always have time to dig the ancient documentation, declare the special types that are compatible with Win32, find the values of the Win32's constants and so on. Nostalgia .Net offers several simple-to-use classes, and components that will allow you to forget about the headache of Win32 and just use the power of Win32 in your application the same way as you use the native. Net classes. More »

Recommended software for developers

    Ultimate Pack     Component pack for Delphi and C++ Builder that contains runtime form designer, runtime object inspector, print suite and much more for the very special price. More »

    Form Designer .Net     Unique runtime form design solution that allows to edit any form in .Net WinForms application at runtime with full source codes for only 300 euro! More »

    Print Suite .Net     Print Suite .Net is a set of components for easy printing texts, images and grids from your WinForms applications. Full C# source codes are available More »

    Gradient Controls .Net     Gradient Controls .Net offers controls with gradient background feature. Labels, panels and so on... Full C# source codes are available More »

    Greatis iGrid     iGrid plots drawing grid right over your desktop, so you can use it everywhere, with any drawing application without any special plugins for different graphic editors. More »

All the contacts and projects

Dmitry Vasiliev (just.dmitry)

More Online Helps

Win32 Programmer's Reference
Win32 Multimedia Programmer's Reference
OLE Programmer's Reference
Microsoft Windows Pen API Programmer's Reference
Microsoft Windows Sockets 2 Reference
Microsoft Windows Telephony API (TAPI) Programmer's Reference
Unix Manual Pages

greatis just4fun network