C，流程，叉

Question

我怎樣才能改變，這樣的功能function_delayed_1和function_delayed_2只進行一次，並同時計劃：

int main(int argc, char *argv[]) { 
    printf("message 1.\n"); 
    fork(); 
    function_delayed_1(); 
    function_delayed_2(); 
    printf("message 2.\n"); 
} 

Answer 1

閱讀man頁面叉的，而谷歌的fork();一些例子,,你的代碼應該像如下：

#include <stdio.h> 
#include <unistd.h> 

int main(int argc, char *argv[]) { 
    pid_t pid; // process ID 

    printf("message 1.\n"); 
    pid = fork(); 
    if (pid < 0) { 
     perror("fork"); 
     return; 
    } 

    if (pid == 0) { 
     function_delayed_1(); // child process 
    } 
    else { 
     function_delayed_2(); // parent process 
    } 
    printf("message 2.\n"); 
} 

Answer 2

int main(int argc, char *argv[]) { 
    printf("message 1.\n"); // printed once by parent process 
    if(fork()) 
     function_delayed_1(); // executed by parent process 
    else 
     function_delayed_2(); // executed by child process 

    printf("message 2.\n"); // will be printed twice once by parent & once by child. 
}