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

#define READBUFSIZE 1024

/* Copy a file one byte at a time */

int main(int argc, char **argv) {
  FILE *fin, *fout;
  char readbuf[READBUFSIZE];

  // Take the filename and number of bytes from command line arguments
  if (argc != 3) {
    fprintf(stderr, "usage: ./cp_example outfile nBytes\n");
    return EXIT_FAILURE;
  }

  // Open the input file
  fin = fopen("/dev/zero", "rb");  // "rb" --> read, binary mode
  if (fin == NULL) {
    perror("fopen for read failed");
    return EXIT_FAILURE;
  }

  // Open the output file
  fout = fopen(argv[1], "wb");  // "wb" --> truncate & write, binary mode
  if (fout == NULL) {
    perror("fopen for write failed");
    return EXIT_FAILURE;
  }

  // Read number of bytes to transfer
  long nBytes;
  if ( sscanf(argv[2], "%ld", &nBytes) != 1 ) {
    fprintf(stderr, "Invalid number of bytes: %s\n", argv[2]);
    return EXIT_FAILURE;
  }

  // Read from the file, write to fout.
  size_t readLen = 0;
  int bytesRemaining = 0;
  for (bytesRemaining=nBytes; bytesRemaining>0; bytesRemaining -= readLen ) {
    size_t bytesToRead = READBUFSIZE < bytesRemaining ? READBUFSIZE : bytesRemaining;
    if ( (readLen = fread(readbuf, 1, bytesToRead, fin)) == 0) break;
    if (fwrite(readbuf, 1, readLen, fout) < readLen) {
      perror("fwrite failed");
      return EXIT_FAILURE;
    }
  }

  // Test to see if we encountered an error while reading.
  if (ferror(fin)) {
    perror("fread failed");
    return EXIT_FAILURE;
  }
  fclose(fin);
  fclose(fout);

  return EXIT_SUCCESS;
}