经典的拷贝文件的代码

#include<sys/stat.h>
#include<fcntl.h>
#include<stdio.h>
#include<errno.h>

#define BUFFER_SIZE 1024

int main(int argc, char **argv)
{
    int from_fd, to_fd;
    int bytes_read, bytes_write;
    char buffer[BUFFER_SIZE];
    char *ptr;

    if(argc != 3)
    {
        fprintf(stderr, "Usage:%s fromfile tofile/n/a", argv[0]);
        exit(1);
    }

    /*打开源文件*/
    if((from_fd = open(argv[1], O_RDONLY)) == -1)
    {
        fprintf(stderr, "Open %s Error:%s/n", argv[1], strerror(errno));
        exit(1);
    }

    /*建立目的文件*/
    if((to_fd = open(argv[2], O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR)) == -1)
    {
        fprintf(stderr, "Open %s Error:%s/n", argv[2], strerror(errno));
        exit(1);
    }

    /*如下代码是一个经典的拷贝文件的代码*/
    while(bytes_read = read(from_fd, buffer, BUFFER_SIZE))
    {
        /*一个致命错误发生了*/
        if((bytes_read == -1) && (errno != EINTR))
            break;
        else if(bytes_read > 0)
        {
            ptr = buffer;
            while(bytes_write = write(to_fd, ptr, bytes_read))
            {
                /*一个致命错误发生了*/
                if((bytes_write == -1) && (errno != EINTR))
                    break;
                /*写完了全部读的字节*/
                else if(bytes_write == bytes_read)
                    break;
                /*只写了一部分继续写*/
                else if(bytes_write > 0)
                {
                    ptr += bytes_write;
                    bytes_read -= bytes_write;
                }
            }
            /*写的时候发生的致命错误*/
            if(bytes_write == -1)
                break;
        }
    }
    close(from_fd);
    close(to_fd);
    exit(0);
}