linux下cp命令的简单实现方法！

linux下cp命令的简单实现方式：

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

#define BUFFERSIZE      4096
#define COPYMODE        0644

int oops(char *, char *);

main(int ac, char *av[])
{
        int     in_fd, out_fd, n_chars;
        char    buf[BUFFERSIZE];
      /* check args  */
        if ( ac != 3 ){
                fprintf( stderr, "usage: %s source destination\n", *av);
                exit(1);
        }
      /* open files */

        if ( (in_fd=open(av[1], O_RDONLY)) == -1 )
                oops("Cannot open ", av[1]);

        if ( (out_fd=creat( av[2], COPYMODE)) == -1 )
                oops( "Cannot creat", av[2]);
 
      /* copy files */

        while ( (n_chars = read(in_fd , buf, BUFFERSIZE)) > 0 )
                if ( write( out_fd, buf, n_chars ) != n_chars )
                        oops("Write error to ", av[2]);
 if ( n_chars == -1 )
   oops("Read error from ", av[1]);

      /* close files */

        if ( close(in_fd) == -1 || close(out_fd) == -1 )
                oops("Error closing files","");
}

int oops(char *s1, char *s2)
{
        fprintf(stderr,"Error: %s ", s1);
        perror(s2);
        exit(1);
}