Binary file I/O using fstreams - why not working?

[Kadence]

I'm trying to use fstreams to read and write binary data to a file with the following code:

#include <fstream>
#include <iostream>
using namespace std;

int main(){
	ofstream out("test.data", ios::binary);
	for(uint i=0; i<10; i++){
		uint outcount = i+100;
		out.write((char*)&outcount, sizeof(uint));
	}
	ifstream in("test.data", ios::binary);
	for(int i=0; i<10; i++){
		uint incount;
		in.read((char*)&incount, sizeof(uint));
		cout << i << " " << incount << endl;
	}
	out.close();
	in.close();
}

However it isn't working for me; it just keeps outputting "10" instead of 100, 101, etc. as I would expect.

What's my mistake?

[Ancient Dragon]

You need to close the output file before opening the input file because some of the data has not been flushed to disk yet.

[Kadence]

Yes that worked, thanks :)

[Kadence]

Another question: what is the purpose of the ios::binary flag? When I try it, the output and input is always binary, even if the flag is omitted and other flags like ios::app are used instead.

[Ancient Dragon]

The binary flag prevents streams from interpreting any of the binary characters (whose character values outside the range of normal printable characters). In normal text files the "\r\n" characters (ms-windows) in the file are used to indicate end-of-line for functions such as getline(). Binary files may also by coincidence have the "\r\n" pair, so the binary flag is used to prevent any interpretion by fstream.

>>and other flags like ios::app are used instead
You can use both flags at the same time by using the or operator | to combine them
ofstream out("test.data", ios::binary | ios::app);