c - fork() 代码

Question

void main ()
{
   if ( fork () )
   {
       printf ( "PID1 %d\n", getpid () );
   }
   else
   {
       printf ( "PID2 %d\n", getpid () );
   }
}

这段代码有什么作用？我知道它与进程 ID 有关，但不应该将某些东西返回到条件中以确定它是否是子/父进程？

Answer 1

一般是:

pid_t pid = fork();
if(pid == 0) {
  //child
} else if(pid > 0) {
  //parent
} else {
 //error
}

手册页说:

RETURN VALUE   Upon successful completion, fork() shall return 0 to the child    process and shall return the process ID of the child process to the    parent process.  Both processes shall continue to execute from    the fork() function.    Otherwise, -1 shall be returned to the parent process, no child process    shall be created, and errno shall be set to indicate the error.