How can I copy a file on Unix using C?

Question

I\'m looking for the Unix equivalent of Win32\'s CopyFile, I don\'t want to reinvent the wheel by writing my own version.

Answer 1

Another variant of the copy function using normal POSIX calls and without any loop. Code inspired from the buffer copy variant of the answer of caf. Warning: Using mmap can easily fail on 32 bit systems, on 64 bit system the danger is less likely.

#include 
#include 
#include 
#include 

int cp(const char *to, const char *from)
{
  int fd_from = open(from, O_RDONLY);
  if(fd_from < 0)
    return -1;
  struct stat Stat;
  if(fstat(fd_from, &Stat)<0)
    goto out_error;

  void *mem = mmap(NULL, Stat.st_size, PROT_READ, MAP_SHARED, fd_from, 0);
  if(mem == MAP_FAILED)
    goto out_error;

  int fd_to = creat(to, 0666);
  if(fd_to < 0)
    goto out_error;

  ssize_t nwritten = write(fd_to, mem, Stat.st_size);
  if(nwritten < Stat.st_size)
    goto out_error;

  if(close(fd_to) < 0) {
    fd_to = -1;
    goto out_error;
  }
  close(fd_from);

  /* Success! */
  return 0;
}
out_error:;
  int saved_errno = errno;

  close(fd_from);
  if(fd_to >= 0)
    close(fd_to);

  errno = saved_errno;
  return -1;
}

EDIT: Corrected the file creation bug. See comment in http://stackoverflow.com/questions/2180079/how-can-i-copy-a-file-on-unix-using-c/2180157#2180157 answer.