1. 使用多进程完成两个文件的拷贝，父进程拷贝前一半，子进程拷贝后一半，父进程回收子进程的资源

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <time.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/wait.h>#define MAXSIZE 1024int main(int argc, char const *argv[])
{pid_t pid = fork();if (0 == pid){usleep(100000);}// 区分父子进程打开 dest 的方式int src = -1, dest = -1;src = open("pm.bmp", O_RDONLY);if (0 != pid){dest = open("pm2.bmp", O_WRONLY|O_CREAT|O_TRUNC, 0664);}else{dest = open("pm2.bmp", O_RDWR|O_APPEND|O_CREAT);}if (-1 == src || -1 == dest){perror("open error");return -1;}// timerstruct timespec start_time = { 0, 0 }, end_time = { 0, 0 };timespec_get(&start_time, TIME_UTC);// 计算文件长度，控制光标位置int file_len = lseek(src, 0, SEEK_END);lseek(src, 0, SEEK_SET);if (0 == pid){lseek(src, file_len / 2, SEEK_SET);lseek(dest, file_len / 2, SEEK_SET);}// 复制int len = 0, count = 0;char buf[MAXSIZE];int bufsize = sizeof(buf);while (count < file_len / 2){if (file_len / 2 - count < bufsize){bufsize = file_len / 2 - count;}len = read(src, buf, bufsize);write(dest, buf, len);count += sizeof(buf);}// timer，计算复制所用时间 (ns)timespec_get(&end_time, TIME_UTC);printf("pid:%d, time:%ld\n", pid, end_time.tv_nsec - start_time.tv_nsec);if (0 == pid){exit(0);}// 等待回收子进程资源wait(NULL);close(src);close(dest);return 0;
}