[Dev-C++] Re: Re: execution of a string with system()

[Christophe C. <chr...@fr...>]

This sample (chunck only) try to copy a file using 'cp' command, and is
thread-safe.
At my knowledge, should run on any Un*x system.

The idea is :
      - create a second process using fork() - this function copy the
current process in a new one. Both processes are then continued from this
point. In the parent process, the return value is the child PID, in the
child it is 0.
      - in the parent process, wait for termination of the child process
(using waitpid()), to synchronize both processes like with a system() call.
      - in the child process, create the command line (command +
parameters) to be executed, and use execve() (or other exec* function) to
replace itself (the code of current process) by the command's code.

#include <unistd.h>           /* For fork() and execvp() */
#include <sys/types.h>        /* For pid_t */
#include <sys/wait.h>         /* For waitpid() */

pid_t PID;              /* The child PID */
int RC=0;               /* The command return code */

...
...
...

PID=fork();             /* Create a new process */
if (PID)                      /* Executed when in the parent process, PID !
= 0 */
{
  waitpid(PID,&RC,0);         /* Wait for termination of the child process
and get its return code */
  if (RC>>8)                  /* Test the return code - many values can be
tested - here, I test only wether it is 0 or not */
  {
    fprintf(stderr,"Error copying file - cp return code [%d]\n",RC>>8);
    exit(EXIT_FAILURE);
  }
  else
    printf"File copied !\n");
}
else                    /* Executed when in the child process, PID == 0 */
{
  char **SysParams=new char *[4];         /* This array will contain the
name of the command, with parameters, terminated by a NULL pointer. This
will be the argv[] array of the called command */
  SysParams[0]="cp";                      /* Command */
  SysParams[1]=InFileName;                /* First param - must be a char *
*/
  SysParams[2]=OutFileName;               /* Second param - must be a char
* */
  SysParams[3]=NULL;                      /* Terminator */
  if (execvp(SysParams[0],SysParams)==-1) /* Replace itself with the
SysParams[0] program, called with SysParams as argv[]
                                        Once exexvp() is started, the
original process is destroyed - it never continues after that point. The
only exception is if execvp() fails (for example if the command can't be
executed).
                                        In this case, we process the
error... I think there are some methods to have a "nice" description of the
error (maybe perror() with errno ?) but I don't know them. */
  {
    fprintf(stderr,"Error in execvp for copying file !\n");
    exit(EXIT_FAILURE);
  }
}

...
...

Good luck in multi-threaded programming !

Christophe