fork和exec一起使用

先预览一下工程的目录树：

实现的功能：master进程启动slave进程。

看看Makefile内容：

all: master.out slave.out

master.out: master.cpp
    g++ master.cpp -o master.out

slave.out: slave.cpp
    g++ slave.cpp -o slave.out

clean:
    rm -rf *.out

master.cpp内容：

/*************************************************************************
    * File: a.cpp
    * Brief:
    * Created Time: Wed 23 Dec 2015 08:50:13 AM CST
 ************************************************************************/

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<iostream>
#include<signal.h>
using namespace std;

#define Sleep(ms) usleep(ms * 1000)

int main(int argc,char* argv[])
{
    printf("pid=%d, ",getpid());
    for(int i=; i<argc;i++)
        printf("[%d]=%s, ",i,argv[i]);
    printf("\n");

    struct sigaction sigchld_action;
    sigchld_action.sa_handler = SIG_DFL;
    sigchld_action.sa_flags = SA_NOCLDWAIT;
    sigaction(SIGCHLD, &sigchld_action, NULL);

    //new process
    int m_subProcessID=fork();
    if (m_subProcessID==)
    {
        int ret=execl("./slave.out","a=abc","b=def","c=12345",NULL);
        if(!=ret)
        {
            printf("execl fails.\n");
            return -;
        }
        printf("execl done wit ok\n");
        return ;
    }
    for(int i=;i<;i++)
    {
        Sleep();
        printf("master say: i=%d\n",i);
    }
    printf("master say: i am done\n");
    return ;
}

slave.cpp内容：

/*************************************************************************
    * File: a.cpp
    * Brief:
    * Created Time: Wed 23 Dec 2015 08:50:13 AM CST
 ************************************************************************/

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<iostream>
#include<signal.h>
using namespace std;

#define Sleep(ms) usleep(ms * 1000)

int main(int argc,char* argv[])
{
    printf("pid=%d, ",getpid());
    for(int i=; i<argc;i++)
        printf("[%d]=%s, ",i,argv[i]);
    printf("\n");

    for(int i=;i<;i++)
    {
        Sleep();
        printf("slave say: -----------------------------------------------------ndex=%d\n",i);
    }
    printf("slave say: i am done\n");
    return ;
}

make编译，看看运行效果：

 [root@localhost testfork]# ./master.out
 pid=, []=./master.out,
 pid=, []=a=abc, []=b=def, []=c=,
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 master say: i=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 master say: i=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 master say: i=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 master say: i=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 master say: i=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 master say: i=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 master say: i=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 master say: i=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 master say: i=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 master say: i=
 master say: i am done
 [root@localhost testfork]# slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: -----------------------------------------------------ndex=
 slave say: i am done

 [root@localhost testfork]# 

可见，在第38行，master正常退出。在第55行，slave也正常退出。

注意到，我们常规启动进程的时候，进程打印的启动参数里面第一个是程序文件名称(也可能包含了路径)。而在这里，我们看到slave.out通过exec函数启动的时候，启动参数里的第一个参数变成了我们在exec函数里设置的参数"a=abc"。

在两个进程都运行的时候，我们查看一下进程信息：

ps -A |grep -sn --color=auto "master\.out\|slave\.out"

master的进程ID为7749，slave的进程ID为7750，两个进程为父子进程。

这里说说fork，在父进程运行到fork时，会分离出一个子进程。两个进程的内存完全一样，子进程会共享父进程当前持有的内核对象，包括互斥量这些同步变量。

例如，父进程打开了一个文件FILE* fp，子进程fclose后，父进程调用fwrite不会报错，但实际上数据并没有写入文件。

资源：

百度网盘\软件源码\testfork.zip

完。