Windows System Programming OpenFile function - c++

Question

The documentation for OpenFile function in Windows is located here. And I am trying to do this:
#include "Tchar.h"
#include <windows.h>
int main(int argc, TCHAR *argv[]){
LPOFSTRUCT _buffer;
HFILE _hfile_ = OpenFile("E:\\mozunit.txt", _buffer, OF_READ);
LPVOID _buffer_read;
LPDWORD _bytes_read;
bool flag = ReadFile(_buffer, _buffer_read, 5, _bytes_read, NULL);
CloseHandle(_buffer);
return 0;
}
Now, when I run this I get an error that I have not initialized the _buffer. So to counter that I initialized _buffer like this:
LPOFSTRUCT _buffer = NULL;
Which gives me an access violation error. Why is that?

Answer 1

According to the documentation, the second argument is...
A pointer to the OFSTRUCT structure that receives information about a file when it is first opened.
By setting it to NULL you're attempting to write to memory with the address of zero.
Try this instead:
OFSTRUCT buffer;
HFILE hfile = OpenFile("E:\\mozunit.txt", &buffer, OF_READ);
char buffer_read[6];
DWORD bytes_read = 0;
bool flag = ReadFile(hfile, &buffer_read, 5, &bytes_read, NULL);
CloseHandle(hfile);

Answer 2

You need to pass a pointer to an allocated LPOFSTRUCT object to OpenFile. You are passing NULL to a function that expects a valid memory, not NULL. You declare an OFSTRUCT object and pass a pointer to it to OpenFile
You have the same issue for the parameters that you pass in ReadFile. And you need to call CloseFile on the _hFile_ file handle, not on the _buffer. The same goes for ReadFile Finally you shouldn't be using OpenFile anyway - you should be using CreateFile as the documentation states.
Your code should be something more like:
#include "Tchar.h"
#include <windows.h>
int main(int argc, TCHAR *argv[]){
OFSTRUCT _buffer = {0}; // Create an OFSTRUCT structure local variable and initialize it to zero.
HFILE _hfile_ = OpenFile("E:\\mozunit.txt", &_buffer, OF_READ);
char _buffer_read[5];
DWORD _bytes_read;
bool flag = ReadFile(_hfile_ , _buffer_read, 5, &_bytes_read, NULL);
CloseHandle(_hfile_ );
return 0;
}