Originální popis anglicky:
pclose - close a pipe stream to or from a process
Návod, kniha: POSIX Programmer's Manual
#include <stdio.h>
int pclose(FILE *
stream);
The
pclose() function shall close a stream that was opened by
popen(), wait for the command to terminate, and return the termination
status of the process that was running the command language interpreter.
However, if a call caused the termination status to be unavailable to
pclose(), then
pclose() shall return -1 with
errno set to
[ECHILD] to report this situation. This can happen if the application calls
one of the following functions:
- *
- wait()
- *
- waitpid() with a pid argument less than or
equal to 0 or equal to the process ID of the command line interpreter
- *
- Any other function not defined in this volume of
IEEE Std 1003.1-2001 that could do one of the above
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.
Upon successful return,
pclose() shall return the termination status of
the command language interpreter. Otherwise,
pclose() shall return -1
and set
errno to indicate the error.
The
pclose() function shall fail if:
- ECHILD
- The status of the child process could not be obtained, as
described above.
The following sections are informative.
None.
None.
There is a requirement that
pclose() not return before the child process
terminates. This is intended to disallow implementations that return [EINTR]
if a signal is received while waiting. If
pclose() returned before the
child terminated, there would be no way for the application to discover which
child used to be associated with the stream, and it could not do the cleanup
itself.
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, IEEE Std 1003.1-2001 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 IEEE Std 1003.1-2001, 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:
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 IEEE Std 1003.1-2001,
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 IEEE Std 1003.1-2001.
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);
}
None.
fork() ,
popen() ,
waitpid() , the Base Definitions volume
of IEEE Std 1003.1-2001,
<stdio.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
