// p3.c —— 原书 Figure 5.3：fork() + wait() + exec()，子进程变身为 wc
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>

int main(int argc, char *argv[]) {
    printf("hello (pid:%d)\n", (int) getpid());
    fflush(stdout);                     // 保证 fork 前缓冲区是空的（见 README "缓冲区陷阱"）
    int rc = fork();
    if (rc < 0) {                       // fork failed; exit
        fprintf(stderr, "fork failed\n");
        exit(1);
    } else if (rc == 0) {               // child (new process)
        printf("child (pid:%d)\n", (int) getpid());
        fflush(stdout);
        char *myargs[3];
        myargs[0] = strdup("wc");       // program: "wc"
        myargs[1] = strdup("p3.c");     // arg: input file
        myargs[2] = NULL;               // mark end of array
        execvp(myargs[0], myargs);      // runs word count
        printf("this shouldn't print out");
    } else {                            // parent goes down this path
        int rc_wait = wait(NULL);
        printf("parent of %d (rc_wait:%d) (pid:%d)\n", rc, rc_wait, (int) getpid());
    }
    return 0;
}