父进程获取子进程退出状态（1） -- 通过信号传递和wait系统调用

main.cpp：

#include <unistd.h>
#include <iostream>
#include <sys/wait.h>
#include <signal.h>
#include <stdlib.h>


using namespace std;

void child_over_callback(int);

void parent_sig_handler(int sig)
{
    cout << "parent catch signal:" << sig << endl;
    if (sig == SIGCHLD) {
        int status;
        pid_t pid;
        pid = wait(&status);
        cout << "parent's child - pid:"<< pid << ",status:" << status << endl;
        if (WIFEXITED(status)) {
            cout << ">> child exited, exit code=" << WEXITSTATUS(status) << endl;
            child_over_callback(sig);
        } else if (WIFSIGNALED(status)) {
            cout << ">> child killed (signal " << WTERMSIG(status) << ")\n";
        } else if (WIFSTOPPED(status)) {
            cout << ">> child stopped (signal " << WSTOPSIG(status) << ")\n";
#ifdef WIFCONTINUED
        } else if (WIFCONTINUED(status)) {
            cout << ">> child continued\n";
#endif
        } else {
            cout << ">> Unexpected status (" << status << ")\n";
        }
    } else {
        cout << ">> child exec error\n";
        exit(1);
    }
}

void child_over_callback(int sig)
{
    cout << "parent signal(" << sig << ") callback\n";
}

int main()
{
    int ret;
    ret = fork();
    if (ret > 0) {
        cout << "parent start\n";
        struct sigaction sa, sa2, oldsa, oldsa2;
        sa.sa_handler = parent_sig_handler;
        sigemptyset(&sa.sa_mask);
        sa.sa_flags = SA_RESTART;
        if (sigaction(SIGCHLD, &sa, &oldsa) == -1) {
            cout << "parent sigaction(SIGCHLD) error\n";
        }
        sa2.sa_handler = parent_sig_handler;
        sigemptyset(&sa2.sa_mask);
        sa2.sa_flags = SA_RESTART;
        if (sigaction(SIGUSR1, &sa2, &oldsa2) == -1) {
            cout << "parent sigaction(SIGUSR1) error\n";
        }
        cout << "parent sleep(40)\n";
        sleep(40);
    } else if (ret == 0) {
        pid_t ppid = getppid();
        cout << "child start\n";
        cout << "child ppid:" << ppid << endl;
        cout << "child pid:" << getpid() << endl;
        cout << "child exec\n";
        if (execl ("./child", "child", (char *)0) < 0) {
            cout << "child exec error\n";
            kill(ppid, SIGUSR1);
        }
    } else {
        cout << "fork error\n";
    }
    return 0;
}

child.cpp：（g++ child.cpp -o child）

#include <unistd.h>
#include <iostream>

using namespace std;

int main()
{
    cout << "child exec start\n";
    cout << "child exec ppid:" << getppid() << endl;
    cout << "child exec pid:" << getpid() << endl;
    sleep(30);
    return 0;
}