Set display before indicate path into (execlp) - c

Question

I need to work with multiple displays in execlp calls (). I'm trying this:
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main()
{
printf("calling to execlp:\n\n");
execlp("DISPLAY=:0 /usr/bin/qtdisplay","qtdisplay", "-r", NULL);
execlp("DISPLAY=:1 /usr/bin/qtdisplay","qtdisplay", "-r", NULL);
printf("fail!");
exit(0);
}
But this fails, with the following message: execlp: No such file or directory
Is there any way to work with the displays?

Answer 1

Try system() instead, it'll start a new child process and call exec() from there. Also, it handles shell command-line constructs by calling a shell and handing your shell construct to that shell, like this:
system("DISPLAY=:0; /usr/bin/qtdisplay -r");
Also, learn to check return codes from functions like this, and do some sane action (like print an error message):
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main()
{
int rc;
rc = system("DISPLAY=:0; /usr/bin/qtdisplay -r");
if (rc == -1) {
perror("error starting qtdisplay on :0");
exit(1);
}
rc = system("DISPLAY=:1; /usr/bin/qtdisplay -r");
if (rc == -1) {
perror("error starting qtdisplay on :1");
exit(1);
}
exit(0);
}
If you want these two commands to be run in parallel (not one after the other), you should use command-lines like this:
system("DISPLAY=:0; /usr/bin/qtdisplay -r &");