Copy a file using copy_file_range

copy.c

/* copy.c
 *
 * Compile with:
 * 
 * gcc copy.c -o copy -Wall -g
 *
 * Defines function copy:
 *
 * Copy a source file to a destination file. If the destination file already
 * exists, this clobbers it. If the destination file does not exist, it is
 * created. 
 *
 * Uses a buffer in user-space, so may not perform as well as 
 * copy_file_range, which copies in kernel-space.
 *
 */

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

#define BUF_SIZE 65536 //2^16

int copy(const char* in_path, const char* out_path){
  size_t n;
  FILE* in=NULL, * out=NULL;
  char* buf = calloc(BUF_SIZE, 1);
  if((in = fopen(in_path, "rb")) && (out = fopen(out_path, "wb")))
    while((n = fread(buf, 1, BUF_SIZE, in)) && fwrite(buf, 1, n, out));
  free(buf);
  if(in) fclose(in);
  if(out) fclose(out);
  return EXIT_SUCCESS;
}

/* Test it out.
 *
 * BASH:
 *
 * gcc copy.c -o copy -Wall -g
 * echo 'Hello, world!' > src.txt
 * ./copy src.txt dst.txt
 * [ -z "$(diff src.txt dst.txt)" ]
 *
 */
int main(int argc, char* argv[argc]){
  if(argc!=3){
    printf("Usage: %s <SOURCE> <DESTINATION>\n", argv[0]);
    exit(EXIT_FAILURE);
  }
  return copy(argv[1], argv[2]);
}