[TOC] ## 创建进程 - fork系统调用是用于创建进程的 - fork创建的进程初始化状态与父进程一样 - 系统会为fork的进程分配新的资源 ## fork 函数 - fork系统调用无参数 - fork会**返回两次**,分别返回子进程id和0 - 返回子进程id的是父进程,返回0的是子进程 ## 示例 <details> <summary>main.cpp</summary> ```#include <iostream> #include <stdio.h> #include <stdlib.h> #include <unistd.h> using namespace std; int main() { int num = 888; pid_t pid; pid = fork(); cout << "fork start" << endl; // pid=0 子进程 if (pid == 0) { cout << "这是一个子进程" << endl; while (true) { num++; cout << "num in son process:" << num << endl; sleep(1); } } // pid>0 父进程,返回子进程ip else if (pid > 0) { cout << "这是一个父进程" << endl; cout << "子进程id: " << pid << endl; while (true) { num--; cout << "num in father process:" << num << endl; sleep(1); } } else if (pid < 0) { cout << "创建进程失败 " << endl; } return 0; } ``` </details> <br /> 编译运行 ``` > g++ main.cpp && ./a.out fork start 这是一个父进程 子进程id: 12543 num in father process:887 fork start 这是一个子进程 num in son process:889 num in son process:890 num in father process:886 num in son process:891 num in father process:885 num in son process:892 num in father process:884 ``` > 相等于子进程 fork