cp命令

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

#define BUFFERSIZE 4096
#define COPYMODE 0644

void oops(char *, char *);

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

if ( ac != 3) //check args
{
fprintf(stderr, "usage: %s source destination ", *av);
exit(1);
}

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

if((out_fd = create(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","");
}

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