How to reopen stdout?

Look:

Code:

---

int main()
{
    FILE *stream,*fp ;
    if((stream = freopen("temp","w",stdout)) == NULL)
    {
      perror("fopen temp error");
      return -1;
    }
    execl("/bin/ls","ls","-l",0);

    freopen("/dev/tty","w",stdout); 
    printf("And now back to the console once again\n");
    fclose(stream);
    return 0;
}

---

I find this statement printf("And now back to the console once again\n")
sometimes it can run,sometimes it cann't run,why?How to correct?

Let's make sure we're on the same page here. What do you expect from the following code?

Code:

---

#include <unistd.h>
#include <stdio.h>
int main(void) {
    execl("/bin/ls", "ls", "-l", 0);
    printf("I'm the Cheshire cat!\n");
    return 0;
}

---

Is that the output you actually get?

Quote:

---

Originally Posted by leetow2003

Look:

Code:

---

int main()
{
    FILE *stream,*fp ;
    if((stream = freopen("temp","w",stdout)) == NULL)
    {
      perror("fopen temp error");
      return -1;
    }
    execl("/bin/ls","ls","-l",0);

    freopen("/dev/tty","w",stdout); 
    printf("And now back to the console once again\n");
    fclose(stream);
    return 0;
}

---

I find this statement printf("And now back to the console once again\n")
sometimes it can run,sometimes it cann't run,why?How to correct?

---

If execl function succeeded then nothing will be executed after statement

Code:

---

    execl("/bin/ls","ls","-l",0);

---

Only if execl failed for any reason than

Code:

---


    freopen("/dev/tty","w",stdout); 
    printf("And now back to the console once again\n");
    fclose(stream);
    return 0;

---

will be executed.

Quote:

---

Originally Posted by tabstop

Let's make sure we're on the same page here. What do you expect from the following code?

Code:

---

#include <unistd.h>
#include <stdio.h>
int main(void) {
    execl("/bin/ls", "ls", "-l", 0);
    printf("I'm the Cheshire cat!\n");
    return 0;
}

---

Is that the output you actually get?

---

Because I want to write to the file via stdout,so I don't use function execl

I'm not sure if you caught what tabstop was saying. When you call execl() (and it succeeds, of course) then your program in memory gets completely replaced with the new one. So any code that occurs after it, won't get executed, ever, at all; not even once that new program finishes running.
For this, fork() first, or use system() instead. (See their respective manual pages for more info)