How to copy a single file to a different partition in Linux, using C

Question

rename (), link() don't work

Thanks!

Answer 1

Have you tried using standard old C functions?

`fopen` the source on one partition
`fopen` the destination on the other partition

LOOP while `fread` > 0
   `fread` from the source to a buff
   `fwrite` to the dest from a buff

And then close your files (ie. fclose).

This is also more portable.

EDIT: If you wanted it to be really basic why not just use a scripting language (python/bash) and get it done in a few lines.

Answer 2

rename() should work. Have you checked the error it returns? rename() returns 0 if it succeeded according to the documentation:

http://www.cplusplus.com/reference/clibrary/cstdio/rename/

You can use perror() to print the error string to standard error (stderr, usually the screen):

http://www.cplusplus.com/reference/clibrary/cstdio/perror/

Answer 3

This is how I would do it. It's pretty simple and leaves the tricky part of the actual copying to the cp tool, which has successfully done this task for several years.

#include <assert.h>
#include <string.h>

#include <sys/wait.h>
#include <unistd.h>

int
runvp(int *ret_status, const char *command, const char * const *argv)
{
  pid_t pid;
  int status;
  char * const *execv_argv;

  pid = fork();
  if (pid == (pid_t) -1)
    return -1;

  if (pid == 0) {
    /*
     * Circumvent the C type conversion rules;
     * see ISO C99: 6.5.16.1#6 for details.
     */
    assert(sizeof(execv_argv) == sizeof(argv));
    memcpy(&execv_argv, &argv, sizeof(execv_argv));

    (void) execvp(command, execv_argv);
    return -1;
  }

  if (waitpid(pid, &status, 0) == -1)
    return -1;

  *ret_status = status;
  return 0;
}

This is a wrapper around fork and execvp that I wrote several years ago. It can be used like this:

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

int main(int argc, char **argv) {
  int exitcode;
  const char *cmdline[] = {
    "cp",
    "--",
    argv[1],
    argv[2],
    NULL
  };

  if (runvp(&exitcode, cmdline[0], cmdline) == -1) {
    perror("runvp");
    return EXIT_FAILURE;
  }
  return EXIT_SUCCESS;
}