_popen, _wpopen
Creates a pipe and executes a command.
Important
This API cannot be used in applications that execute in the Windows Runtime. For more information, see CRT functions not supported in Universal Windows Platform apps.
Syntax
FILE *_popen(
const char *command,
const char *mode
);
FILE *_wpopen(
const wchar_t *command,
const wchar_t *mode
);
Parameters
command
Command to be executed.
mode
Mode of the returned stream.
Return value
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. If the error is caused by an invalid parameter, errno is set to EINVAL. See the Remarks section for valid modes.
For information about these and other error codes, see errno, _doserrno, _sys_errlist, and _sys_nerr.
Remarks
The _popen function creates a pipe. It then asynchronously executes a spawned copy of the command processor, and uses command as the command line. The character string mode specifies the type of access requested, as follows.
| Access mode | Description |
|---|---|
"r" |
The calling process can read the spawned command's standard output using the returned stream. |
"w" |
The calling process can write to the spawned command's standard input using the returned stream. |
"b" |
Open in binary mode. |
"t" |
Open in text mode. |
Note
If used in a Windows program, the _popen function returns an invalid file pointer that causes the program to stop responding indefinitely. _popen works properly in a console application. To create a Windows application that redirects input and output, see Creating a child process with redirected input and output in the Windows 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.
By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.
Generic-text routine mappings
Tchar.h routine |
_UNICODE and _MBCS not defined |
_MBCS defined |
_UNICODE defined |
|---|---|---|---|
_tpopen |
_popen |
_popen |
_wpopen |
Requirements
| Routine | Required header |
|---|---|
_popen |
<stdio.h> |
_wpopen |
<stdio.h> or <wchar.h> |
For more compatibility information, see Compatibility.
Libraries
All versions of the C run-time libraries.
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>
int main(void)
{
char psBuffer[128];
FILE* pPipe;
/* 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 ((pPipe = _popen("dir *.c /on /p", "rt")) == NULL)
{
exit(1);
}
/* Read pipe until end of file, or an error occurs. */
while (fgets(psBuffer, 128, pPipe))
{
puts(psBuffer);
}
int endOfFileVal = feof(pPipe);
int closeReturnVal = _pclose(pPipe);
if (endOfFileVal)
{
printf("\nProcess returned %d\n", closeReturnVal);
}
else
{
printf("Error: Failed to read the pipe to the end.\n");
}
}
This output assumes there's only one file in the current directory that has a .c file name extension.
Volume in drive C is CDRIVE
Volume Serial Number is 0E17-1702
Directory of D:\proj\console\test1
07/17/98 07:26p 780 popen.c
1 File(s) 780 bytes
86,597,632 bytes free
Process returned 0