Thread: Issues with writing data to binary files

Im trying to write my custom file encrypter, but the outfile fp2 is empty so I'm doing something wrong here:

Code:

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

#defineSIZE(a) sizeof(a) / sizeof(a[0])

void encrypt(const char *fileName, const char *newFileName, const char *KWORD,
             int K)
{
  FILE *fp, *fp2;
  fp = fopen(fileName, "rb");
  fp2 = fopen(newFileName, "a+");
  if (!fp) {
    printf("\nError: Could not open the file %s\n", fileName);
  } else {
    printf("\nFile has been opened successfully\n");

    int block[8192], xorblock[8192];
    char banner[128];

    size_t allBytes, byteCount =
        fread(banner, sizeof(banner), sizeof(banner), fp);
    printf("BASE FILE BANNER: %s\n", banner);
    fseek(fp, 0, SEEK_SET);

    while (byteCount) {
      byteCount = fread(block, sizeof(block), sizeof(block), fp);
      allBytes += byteCount;
      printf("\rByte has been read: %zu\r", byteCount);

      for (size_t i = 0; i < SIZE(block); i++) {
        K = K % strlen(KWORD);
        volatile char kwordPos = KWORD[K];
        xorblock = block ^ (int) kwordPos;
        K++;
      }
      fwrite(xorblock, sizeof(xorblock), sizeof(xorblock), fp2);
    }
    printf("\nAll bytes read:%zu\n", allBytes);

  }
  fclose(fp);
  fclose(fp2);

  FILE *fp2read;
  fp2read = fopen(newFileName, "rb");
  char newBanner[128];
  fread(newBanner, sizeof(newBanner), sizeof(newBanner), fp2read);
  printf("\nNEW FILE BANNER: %s\n", newBanner);
}

int main()
{
  const char *myFileName = "Example.txt";
  char newFileName[17] = "_NEW_";
  const char *keyWord = "Keyword";
  int Key = 'K';

  strcat(newFileName, myFileName);
  encrypt(myFileName, newFileName, keyWord, Key);
  printf("%s%zu\n", newFileName, strlen(newFileName));
  printf("\nAll done.Quitting now.\n");
  return 0;
}

fsanitizer is showing that something is crashing pretty badly:

File has been opened successfullyBASE FILE BANNER: C plus plus


All bytes read:0
AddressSanitizer:DEADLYSIGNAL
================================================== ===============
==571==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7f2229726005 bp 0x7ffe1b18abe0 sp 0x7ffe1b18a320 T0)
==571==The signal is caused by a READ memory access.
==571==Hint: address points to the zero page.
AddressSanitizer:DEADLYSIGNAL
AddressSanitizer: nested bug in the same thread, aborting.