cp命令的实现

#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>

#define BUFFERSIZE 4096
#define COPYMODE   0644

void oops(char *, char *);

int main(int argc, char *argv[])
{
    int in_fd, out_fd, n_chars;
    char buf[BUFFERSIZE];

    if (argc != 3)
    {   
        fprintf(stderr, "Usage: %s source destination\n", *argv);
        exit(1);
    }   

    if ((in_fd = open(argv[1], O_RDONLY)) == -1)
        oops("Cannot open ", argv[1]);
    
    if ((out_fd = creat(argv[2], COPYMODE)) == -1)
        oops("Cannot creat ", argv[2]);
    
    while ((n_chars = read(in_fd, buf, BUFFERSIZE)) > 0)
    {   
        if (write(out_fd, buf, n_chars) != n_chars)
        {   
            oops("Write error to ", argv[2]);
        }   
    }   

    if (n_chars == -1)
        oops("Read error from ", argv[1]);

    if (close(in_fd) == -1 || close(out_fd) == -1)  
        oops("Error closing files", "");
    return 0;
}
void oops(char *s1, char *s2)
{
    fprintf(stderr, "Error: %s", s1);
    perror(s2);
    exit(1);
}