Linux下__ファイルコピー_C言語

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>

int main(void) 
{ 
    const char *pathName = "f.c"; 
    int in, out, flag; 
    char buffer[1024];
    
    in = open("z.c", O_RDONLY, S_IRUSR);
    if (-1 == in) //       ,     
    {    
        printf("open file z.c error !
");
        return -1;
    }
    
    out = creat(pathName, S_IWUSR);
    if (-1 == in) //       ,     
    {
        printf("create file %s error !
", pathName);
        return -1;
    }
    
    while ((flag = read(in, buffer, 1024)) > 0)
    { 
        write(out, buffer, flag);
    }
    
    close(in);
    close(out);
    printf("copy file z.t to %s finish !
", pathName);
    
    return 0;
}