Output / input stream of external program

[RenaiCompix]

Hi!
I want to build a software that's able to start a certain process.
The software must be able to get every output of this process and send input to this process somehow. (The process sends std::cout 's and wants some std::cin 's)

Is there any way to handle this task?

[kbw]

That's pretty standard on Unix, there are lots of examples available. What platform are you using?

[RenaiCompix]

I'm using Ubuntu / Debian. But I haven't found anything useful until now, because what I know system(); couldn't handle this task, because it returns the integer of the main function. If completed.

[RenaiCompix]

I found something working in C, but is there a better way using STL of C++ than this one:

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

int main(){

	pid_t pid;
	int rv;
	int	commpipe[2];		/* This holds the fd for the input & output of the pipe */

	/* Setup communication pipeline first */
	if(pipe(commpipe)){
		fprintf(stderr,"Pipe error!\n");
		exit(1);
	}

	/* Attempt to fork and check for errors */
	if( (pid=fork()) == -1){
		fprintf(stderr,"Fork error. Exiting.\n");  /* something went wrong */
		exit(1);        
	}

	if(pid){
		/* A positive (non-negative) PID indicates the parent process */
		dup2(commpipe[1],1);	/* Replace stdout with out side of the pipe */
		close(commpipe[0]);		/* Close unused side of pipe (in side) */
		setvbuf(stdout,(char*)NULL,_IONBF,0);	/* Set non-buffered output on stdout */
		sleep(2);
		printf("Hello\n");
		sleep(2);
		printf("Goodbye\n");
		sleep(2);
		printf("exit\n");
		wait(&rv);				/* Wait for child process to end */
		fprintf(stderr,"Child exited with a %d value\n",rv);
	}
	else{
		/* A zero PID indicates that this is the child process */
		dup2(commpipe[0],0);	/* Replace stdin with the in side of the pipe */
		close(commpipe[1]);		/* Close unused side of pipe (out side) */
		/* Replace the child fork with a new process */
		if(execl("child","child",NULL) == -1){
			fprintf(stderr,"execl Error!");
			exit(1);
		}
	}
	return 0;
}

[Sajjad Heydari]

i found a silly way, run this command:
system("app > resault.txt")
then u need to read resault.txt from the parent app.

[kbw]

I think that's a good example.

STL can't really help with the actual pipe management. GCC used to have a vendor specific extension to the IO Stream library that allowed you to construct an fstream from a file descriptor, but that's not standard so I'd avoid it.

[ne555]

There is boost, however. Look for file descriptor.

By the way, use perror when system calls fail. It reads errno, so you get a message of what went wrong