Writing zeroes to file block does not work - c++

Question

So I'm trying to write a sequence of zeroes from a file offset until the end of the file, here is my code:
HANDLE hFile = CreateFileA((LPCSTR)"hello.txt", GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
if(hFile < 0) return -1;
DWORD fileSize = GetFileSize(hFile, NULL);
DWORD offset = 0x13d4;
DWORD check = NULL;
DWORD pos = SetFilePointer(hFile, offset, 0, FILE_BEGIN);
BYTE* zeroes = new BYTE[fileSize-offset];
ZeroMemory((PVOID)zeroes, fileSize-offset);
WriteFile(hFile, (PVOID)&zeroes, fileSize-offset, &check, NULL);
printf("Wrote %d bytes at %x\n", check, pos);
if(check < fileSize-offset)
{
printf("[+] An error occured while trying to patch the file.");
return EXIT_FAILURE;
}
CloseHandle(hFile);
Now I checked my fileSize is correct, the file offset (pos) is the same as offset, my file Handle is valid, the number of bytes written stored in check is equal to the the zeroes buffer length and the last error is 0. However, when I check my file in hex mode it did not add any zeroes at the end.
Any ideas?
Thanks in advance

Answer 1

The line
WriteFile(hFile, (PVOID)&zeroes, fileSize-offset, &check, NULL);
is wrong. You are writing data in the pointer variable zeroes itself, not what is pointed at by the variable. Typically the pointer has only 4 or 8 bytes, so it may cause out-of-range access if the file is large enough.
Remove & before zeros to have it write contents of the buffer pointed at by zeroes.
WriteFile(hFile, (PVOID)zeroes, fileSize-offset, &check, NULL);