#include <stdio.h> int pclose(FILE *stream);
In any case, pclose() shall not return before the child process created by popen() has terminated.
If the command language interpreter cannot be executed, the child termination status returned by pclose() shall be as if the command language interpreter terminated using exit(127) or _exit(127).
The pclose() function shall not affect the termination status of any child of the calling process other than the one created by popen() for the associated stream.
If the argument stream to pclose() is not a pointer to a stream created by popen(), the result of pclose() is undefined.
If a thread is canceled during execution of pclose(), the behavior is undefined.
The following sections are informative.
If the stream pointed to by stream was not created by popen(), historical implementations of pclose() return -1 without setting errno. To avoid requiring pclose() to set errno in this case, POSIX.1-2008 makes the behavior unspecified. An application should not use pclose() to close any stream that was not created by popen().
Some historical implementations of pclose() either block or ignore the signals SIGINT, SIGQUIT, and SIGHUP while waiting for the child process to terminate. Since this behavior is not described for the pclose() function in POSIX.1-2008, such implementations are not conforming. Also, some historical implementations return [EINTR] if a signal is received, even though the child process has not terminated. Such implementations are also considered non-conforming.
Consider, for example, an application that uses:
popen("command", "r")
to start command, which is part of the same application. The parent writes a prompt to its standard output (presumably the terminal) and then reads from the popen()ed stream. The child reads the response from the user, does some transformation on the response (pathname expansion, perhaps) and writes the result to its standard output. The parent process reads the result from the pipe, does something with it, and prints another prompt. The cycle repeats. Assuming that both processes do appropriate buffer flushing, this would be expected to work.
To conform to POSIX.1-2008, pclose() must use waitpid(), or some similar function, instead of wait().
The code sample below illustrates how the pclose() function might be implemented on a system conforming to POSIX.1-2008.
int pclose(FILE *stream)
{
int stat;
pid_t pid;
pid = <pid for process created for stream by popen()>
(void) fclose(stream);
while (waitpid(pid, &stat, 0) == -1) {
if (errno != EINTR){
stat = -1;
break;
}
}
return(stat);
}
The Base Definitions volume of POSIX.1-2017, <stdio.h>
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