Where fork is prone to errors

Today, I found an interesting piece of code while reading the code.

#include<stdio.h>#include<stdlib.h>#include<unistd.h>#include<sys/types.h>int main(){        int pid=1;        if(pid=fork()<0)        {                perror("fork() error!\n");                exit(-1);        }        else if(pid==0)        {                printf("child  pid[%d]\n",getpid());                sleep(15);        }        else        {                printf("parents pid[%d]\n",getpid());                sleep(15);        }        return 0;}

First, let's guess what the execution result of this code is?

It looks very simple. Many people say the results are as follows:

Child PID [% d]
Parents PID [% d]

 

The result is as follows:

Child PID [% d]

Child PID [% d]

 

If the code is changed to If (pid = fork () <0)

The results are as expected:

Child PID [% d]
Parents PID [% d]

 

The reason is the operator priority.

Because the priority of the operator '<' is higher than that of the operator '=. Therefore, the PID obtains the result of the comparison expression (Fork () <0 ). This result is false, so pid = 0. Therefore, both the parent and child processes output the child PID [% d].

Where fork is prone to errors