Question

Suppose I do a system("ps-C nautilus"); how do I return the result of this function in char* ?

Thank you.

Answer 1

If your compiler supports some variant of popen() you can redirect the output fairly easily.

Caveats:

1. The code below was written on a Windows box, which uses _popen() instead of popen(). It is not hard to convert for *nix.
2. The code below has no error handling. It is just intended to illustrate the technique. You must add error checking before using it in production.
3. This all runs in one thread. If the program was likely to run for a long time, you might need to use a second thread to read its output while it runs.
4. I think popen() is POSIX, which means it will work on most *nix boxes, but it is not standard C, so should not be considered portable.

char *RunProg(const char *szCmdLine)
{
  size_t nSize=512;
  size_t nUsed=0;
  char *szOut = malloc(nSize);
  FILE *fp = _popen(szCmdLine, "r");
  char szBuff[128];
  while( !feof( fp ) )
  {
      if( fgets( szBuff, sizeof(szBuff), fp ) != NULL )
      {
          nUsed += strlen(szBuff);
          if (nUsed >= nSize)
          {
              nSize += nUsed;
              szOut = realloc(szOut, nSize);
          }
          strcat(szOut, szBuff);
      }
  }
  _pclose(fp);
  return szOut;
}