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I implemented the following two pieces of code. Why is the number of printf executions in the two pieces of code not equal, one is 6 times and the other is 8 times? My system and GCC version information is as follows：

root#lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 18.04.6 LTS
Release:        18.04
Codename:       bionic
root#gcc --version
gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

code 1:

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
int main(void)
{
        int i = 0;
        for (;i < 2; i++)
        {
                fork();
                printf(" i = %d\n", i);
        }
        return 0;
}
root#gcc test_fork.c
root#./a.out
 i = 0
 i = 1
 i = 0
 i = 1
 i = 1
root# i = 1

code 2:

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
int main(void)
{
        int i = 0;
        for (;i < 2; i++)
        {
                fork();
                printf("=");
        }
        return 0;
}

root#gcc test_fork.c
root#./a.out
========
yanzhang92
  • 15
  • 3
  • Pretty sure it's this one. There are several variations on how to trigger this, depending on what kind of buffering is the default, but an explicit flush should always fix it. If it doesn't, you have some other bug. – o11c Dec 07 '21 at 05:36

0 Answers0