Writing integer to binary file using C++?

Question

I have a very simple question, which happens to be hard for me since this is the first time I tried working with binary files, and I don't quite understand them. All I want to do is write an integer to a binary file.

Here is how I did it:

#include <fstream>
using namespace std;
int main () {
    int num=162;
    ofstream file ("file.bin", ios::binary);
    file.write ((char *)&num, sizeof(num));
    file.close (); 
    return 0;
}

Could you please tell me if I did something wrong, and what?

The part that is giving me trouble is line with file.write, I don't understand it.

Thank you in advance.

Answer 1

The part that is giving me trouble is line with file.write, I don't understand it.

If you read the documentation of ofstream.write() method, you'll see that it requests two arguments:

1. a pointer to a block of data with the content to be written;

2. an integer value representing the size, in bytes, of this block.

This statement just gives these two pieces of information to ofstream.write():

file.write(reinterpret_cast<const char *>(&num), sizeof(num));

&num is the address of the block of data (in this case just an integer variable), sizeof(num) is the size of this block (e.g. 4 bytes on 32-bit platforms).