Initiates a pipe to a process.
Format
#include <stdio.h>
FILE *popen (const char *command, const char
*type);
Arguments
- command
- A pointer to a null-terminated string containing a shell
command line.
- type
- A pointer to a null-terminated string containing an I/O mode.
Because open files are shared, you can use a type r command as an
input filter and a type w command as an output filter. Specify one
of the following values for the type argument:
- r - the calling program can read from the standard output
of the command by reading from the returned file stream.
- w - the calling program can write to the standard
input of the command by writing to the returned file stream.
Description
This function creates a pipe between the calling program and
a shell command awaiting execution. It returns a pointer to a FILE
structure for the stream.
- Note
- When you use the popen function
to invoke an output filter, beware of possible deadlock caused by
output data remaining in the program buffer. You can avoid this by
either using the setvbuf function to ensure that the output stream
is unbuffered, or the fflush function to ensure that all buffered
data is flushed before calling the pclose function.
See also fflush, pclose, and setvbuf in this section.
Return Values
| x | A pointer to the FILE structure
for the opened stream. |
| NULL |
Indicates an error. Unable to create files or processes.
|
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