[TOC] ## 創建進程 - fork系統調用是用于創建進程的 - fork創建的進程初始化狀態與父進程一樣 - 系統會為fork的進程分配新的資源 ## fork 函數 - fork系統調用無參數 - fork會**返回兩次**,分別返回子進程id和0 - 返回子進程id的是父進程,返回0的是子進程 ## 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 子進程 if (pid == 0) { cout << "這是一個子進程" << endl; while (true) { num++; cout << "num in son process:" << num << endl; sleep(1); } } // pid>0 父進程,返回子進程ip else if (pid > 0) { cout << "這是一個父進程" << endl; cout << "子進程id: " << pid << endl; while (true) { num--; cout << "num in father process:" << num << endl; sleep(1); } } else if (pid < 0) { cout << "創建進程失敗 " << endl; } return 0; } ``` </details> <br /> 編譯運行 ``` > g++ main.cpp && ./a.out fork start 這是一個父進程 子進程id: 12543 num in father process:887 fork start 這是一個子進程 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 ``` > 相等于子進程 fork