How can I run an external program from C and parse its output?

Question

I've got a utility that outputs a list of files required by a game. How can I run that utility within a C program and grab its output so I can act on it within the same program?

UPDATE: Good call on the lack of information. The utility spits out a series of strings, and this is supposed to be portable across Mac/Windows/Linux. Please note, I'm looking for a programmatic way to execute the utility and retain its output (which goes to stdout).

Answer 1

As others have pointed out, popen() is the most standard way. And since no answer provided an example using this method, here it goes:

#include <stdio.h>  #define BUFSIZE 128  int parse_output(void) {     char *cmd = "ls -l";              char buf[BUFSIZE];     FILE *fp;      if ((fp = popen(cmd, "r")) == NULL) {         printf("Error opening pipe!\n");         return -1;     }      while (fgets(buf, BUFSIZE, fp) != NULL) {         // Do whatever you want here...         printf("OUTPUT: %s", buf);     }      if (pclose(fp)) {         printf("Command not found or exited with error status\n");         return -1;     }      return 0; } 

Sample output:

OUTPUT: total 16 OUTPUT: -rwxr-xr-x 1 14077 14077 8832 Oct 19 04:32 a.out OUTPUT: -rw-r--r-- 1 14077 14077 1549 Oct 19 04:32 main.c 

Answer 2

For simple problems in Unix-ish environments try popen().

From the man page:

The popen() function opens a process by creating a pipe, forking and invoking the shell.

If you use the read mode this is exactly what you asked for. I don't know if it is implemented in Windows.

For more complicated problems you want to look up inter-process communication.