使用 fork 后，可能需要获取 fork 的进程的运行状况，比如有没有异常、崩溃。

wait 在 man 中关键的描述如下：

All  of  these system calls are used to wait for state changes in a child of the calling process, and obtain information about the child whose state has changed.  A state change is considered to be: the child terminated; the child was stopped by a signal; or the child was resumed by a signal.

#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <sys/types.h>#include <sys/wait.h>int main(void){    pid_t pid;    int status;    printf("before fork\n");    fflush(stdout);    if ( (pid = fork()) < 0)    {        printf("fork error\n");    }    else if (pid == 0)    {        printf("after fork, child\n");        // 4种测试情况        exit(7); // -> normal termination, exitstatus = 7        // abort(); // -> abnormal termination, signalstatus = 6 (SIGABRT)        // int i = 1 / 0; // -> abnormal termination, signalstatus = 8 (SIGFPE)        // char *p = NULL; *p = 'a'; // -> abnormal termination, signalstatus = 11 (SIGSEGV)    }    wait(&status);        if (WIFEXITED(status))    {        printf("normal termination, exitstatus = %d\n", WEXITSTATUS(status));    }    else if (WIFSIGNALED(status))    {        printf("abnormal termination, signalstatus = %d\n", WTERMSIG(status), #ifdef WCOREDUMP        WCOREDUMP(status)?"(core file generated)":""); #else        "");#endif    }    else if (WIFSTOPPED(status))    {        printf("child stopped, signal number = %d\n", WSTOPSIG(status));    }    printf("after fork, parent\n");    return 0;}