_popen, _wpopen

Creates a pipe and executes a command.

FILE*_popen(constchar*command,constchar*mode);

FILE*_wpopen(constwchar_t*command,constwchar_t*mode);

For additional compatibility information, see Compatibility in the Introduction.

Libraries

Return Value

Each of these functions returns a stream associated with one end of the created pipe. The other end of the pipe is associated with the spawned command’s standard input or standard output. The functions return NULL on an error.

Parameters

command

Command to be executed

mode

Mode of returned stream

Remarks

The _popen function creates a pipe and asynchronously executes a spawned copy of the command processor with the specified string command. The character string mode specifies the type of access requested, as follows:

"r"

The calling process can read the spawned command’s standard output via the returned stream.

"w"

The calling process can write to the spawned command’s standard input via the returned stream.

"b"

Open in binary mode.

"t"

Open in text mode.

Note   The _popen function returns an invalid file handle, if used in a Windows program, that will cause the program to hang indefinitely. _popen works properly in a Console application. To create a Windows application that redirects input and output, read the section "Creating a Child Process with Redirected Input and Output" in the Win32 SDK.

_wpopen is a wide-character version of _popen; the path argument to _wpopen is a wide-character string. _wpopen and _popen behave identically otherwise.

Generic-Text Routine Mappings

Example

/* POPEN.C: This program uses _popen and _pclose to receive a
 * stream of text from a system process.
 */

#include <stdio.h>
#include <stdlib.h>

void main( void )
{

   char   psBuffer[128];
   FILE   *chkdsk;

        /* Run DIR so that it writes its output to a pipe. Open this
    * pipe with read text attribute so that we can read it
         * like a text file.
    */
   if( (chkdsk = _popen( "dir *.c /on /p", "rt" )) == NULL )
      exit( 1 );

   /* Read pipe until end of file. End of file indicates that
    * CHKDSK closed its standard out (probably meaning it
         * terminated).
    */
   while( !feof( chkdsk ) )
   {
      if( fgets( psBuffer, 128, chkdsk ) != NULL )
         printf( psBuffer );
   }

   /* Close pipe and print return value of CHKDSK. */
   printf( "\nProcess returned %d\n", _pclose( chkdsk ) );
}

Output

 Volume in drive C is CDRIVE
 Volume Serial Number is 0E17-1702

 Directory of C:\dolphin\crt\code\pcode

05/02/94  01:05a                   805 perror.c
05/02/94  01:05a                 2,149 pipe.c
05/02/94  01:05a                   882 popen.c
05/02/94  01:05a                   206 pow.c
05/02/94  01:05a                 1,514 printf.c
05/02/94  01:05a                   454 putc.c
05/02/94  01:05a                   162 puts.c
05/02/94  01:05a                   654 putw.c
               8 File(s)          6,826 bytes
                             86,597,632 bytes free

Process returned 0

Process and Environment Control Routines

See Also   _pclose, _pipe