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On UNIX-based systems, child processes are typically spawned using a form of fork() and exec(), and the child process always receives copies of its parent's file descriptors. Under Microsoft Windows, the CreateProcess() function is typically used to start a child process. In Windows, file-handle inheritance is determined on a per-file basesbasis. Additionally, the CreateProcess() function itself provides a mechanism to limit file-handle inheritance. As a result, the child process spawned by CreateProcess() may not receive copies of the parent process's open file handles.
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Sometimes it is not practical for a program to close all active file descriptors before issuing a system call such as system() or exec(). An alternative on POSIX systems is to use the new line FD_CLOEXEC flag, or O_CLOEXEC when available, to set the close-on-exec flag for the file descriptor.
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