fork函数简介
作用
创建一个子进程。
原型
pid_t fork(void)
返回值
失败返回-1；成功返回：① 父进程返回子进程的ID ②子进程返回 0
pid_t类型表示进程ID，但为了表示-1，它是有符号整型。(0不是有效进程ID，init最小，为1)
（注意返回值，不是fork函数能返回两个值，而是fork后，fork函数变为两个，父子需【各自】返回一个。）
创建一个子进程
#include <stdio.h> #include <unistd.h> #include <sys/types.h> int count = 100; int main(int argc, const char* argv[]) { pid_t pid; printf("start: \n"); pid = fork(); if(pid > 0) { printf("I am a parent process, count = %d, pid = %d\n", count,getpid()); count += 10; printf("I am a parent process, count = %d, pid = %d\n", count,getpid()); } else if(pid == 0) { printf("I am a child process, count = %d, pid = %d\n", count,getpid()); count += 1; printf("I am a child process, count = %d, pid = %d\n", count,getpid()); } printf("finish!\n"); return 0; }
循环的创建多个兄弟子进程
#include <stdio.h> #include <unistd.h> #include <sys/types.h> int count = 100; int main(int argc, const char* argv[]) { pid_t pid; int i = 0; int n = 2; for(; i < n; i++) { pid = fork(); if(pid == 0) { break; } } if(i == 0) { printf("I am the first child process, pid = %d\n", getpid()); } else if(i == 1) { printf("I am the second child process, pid = %d\n", getpid()); } else if(i == 2) { printf("I am the parent process, pid = %d\n", getpid()); } else { printf("error\n"); } return 0; }