子进程无法写入文件？

Question

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <errno.h>

int main() {
  FILE *f = fopen("stories.txt", "w");


  if (!f) {
    error("Can't open stories.txt");
  }

  pid_t pid = fork();
  if (pid == -1) {
    error("Can't fork process");
  }

  if (!pid) {     

    fprintf(f, "f---- child process wrote\n");

    printf("---- child process wrote\n");

    if (execl("/bin/ls", "/bin/ls", NULL) == -1) {
        error("Can't run script");
    }

  }

  fprintf(stdout, "parent process wrote it after fork!\n");
  fprintf(f, "parent process wrote it before return main!\n");
  return 0;
}

When I run the above code in Ubuntu Linux 64-bit, this

        fprintf(f, "f---- child process wrote\n");

is not written in the stories.txt file.

Can you help me explain why this happens?

When I comment out the execl then the write to the file from the child process is done OK.

Answer 1

use fclose(f); before run execl

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <errno.h>

int main() {
  FILE *f = fopen("stories.txt", "w");


  if (!f) {
    error("Can't open stories.txt");
  }

  pid_t pid = fork();
  if (pid == -1) {
    error("Can't fork process");
  }

  if (!pid) {     

    fprintf(f, "f---- child process wrote\n");

    printf("---- child process wrote\n");
    fclose(f);
//--^^^^^^^^^^--//
    if (execl("/bin/ls", "/bin/ls", NULL) == -1) {
        error("Can't run script");
    }


    exit(0);
  }

  fprintf(stdout, "parent process wrote it after fork!\n");
  fprintf(f, "parent process wrote it before return main!\n");
  return 0;
}