C++使用map实现多进程拷贝文件的程序思路

#include <iostream>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <cstring>

int main(int argc, char *argv[])
{   
    //1. 指定创建子进程的个数
    int proNum = 5;

    //2. 打开源文件
    int fd_r = open(argv[1], O_RDONLY);
    if(fd_r == -1){
        std::cout << "open error" << std::endl;
        exit(1);
    }
    //3. 打开目的文件, 不存在则创建
    int fd_w = open(argv[2], O_RDWR|O_CREAT|O_TRUNC, 0666);
    if(fd_w == -1){
        std::cout << "open error" << std::endl;
        exit(1);
    }
    /*4. 获取文件大小
     *--------------
     * 相比于seek速度更快
     * */
    struct stat statbuf;
    stat(argv[1], &statbuf);
    int size = statbuf.st_size;
    //5. 根据文件大小拓展目标文件
    int ret = ftruncate(fd_w, size);
    if(ret == -1){
        std::cout << "ftruncate error" << std::endl;
        exit(1);
    }
    std::cout << argv[1] <<"的文件大小为：" << size << std::endl;
    //6. 为源文件创建映射
    char *mmp_r = (char *)mmap(NULL, size, PROT_READ, MAP_SHARED, fd_r, 0);
    if(mmp_r == MAP_FAILED){
        std::cout << "mmap error" << std::endl;
        exit(1);
    }

    close(fd_r);
    //7. 为目标文件创建映射
    char *mmp_w = (char *)mmap(NULL, size, PROT_WRITE, MAP_SHARED, fd_w, 0);
    if(mmp_w == MAP_FAILED){
        std::cout << "mmap error" << std::endl;
        exit(1);
    }
    //8. 求出每个子进程该拷贝的字节数
    int size_sp = size / proNum;
    int size_sle = size % proNum;
    //9. 创建N个子进程
    int i;
    for(i=0; i<proNum ; ++i){
        pid_t pid = fork();
        if(pid == -1){
            std::cout << "fork error" << std::endl;
            exit(1);
        }else if(pid == 0){ // 子进程
            /* 拷贝文件内容 */
            if(i < proNum - 1)
            {
                memcpy(mmp_w+i*size_sp, mmp_r+i*size_sp, size_sp);
                std::cout << "我是进程" << i << "拷贝文件大小为：" << size_sp<< std::endl;
            }
            else{
                memcpy(mmp_w+i*size_sp, mmp_r+i*size_sp, size_sp+size_sle);
                std::cout << "我是进程" << i << "拷贝文件大小为：" << size_sp+size_sle << std::endl;
            }
            break;
        }
    }
    munmap(mmp_r, size);
    munmap(mmp_w, size);

    return 0;
}