/**
*exec_execve.c
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>

int main(int argc, char * const argv[], char ** environ) {
    /* code */
    pid_t    pid;
    int        stat_val;

    printf("%s\n", "Exec example");
    pid = fork();

    switch( pid ) {
        case 0:
            printf("%s\n", "Child process is running now");
            printf("My pid is:%d, My ppid is:%d\n", getpid(), getppid());
            printf("My uid is:%d, My gid is:%d\n", getuid(), getgid());

            //execve函数（const char * path, char * const argv[], char * const envp[]）
            //执行另外一个程序，进程就是当前的子进程，即当前的子进程执行了一个新的程序
            execve("processimage", argv, environ);

            //当调用新的可执行程序之后，原有的子进程的映像被替换掉了，不再被执行，子进程永远不会执行到
            //下面这条语句
            printf("%s\n", "process never go to here");
            exit(0);

        case -1:
            perror("process create failed\n");
            //失败返回1
            exit(1);
            
        default:    //剩余的就是子进程的进程号
            printf("parent process is running and pid is %d\n", getpid());
            break;
    }

    wait(&stat_val);
    exit(0);
}

/*
 * processimage.c
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>

int main(int argc, char const *argv[], char ** environ) {
  /* code */
  int i;

  printf("%s\n", "I am process image");
  printf("My pid is:%d, My pid is:%d\n", getpid(), getppid());
  printf("My uid is:%d, My gid is:%d\n", getuid(), getgid());

  for (i = 0; i < argc; i++) {
    printf("argv[%d] is: %s\n", i, argv[i]);
  }
  
  return 0;
}

gcc -o exec_execve exec_execve.c
gcc -o processimage processimage.c

./exec_execve test execve