Binary I/O - Partially Truncated output

[leourb]

I have written a little program to test binary I/O from a simple text.

My program works but when I compare the imported and the exported files, in this last 2 chars are "missing".

Why?

Thanks!

Source file:

#include "stdafx.h"
#include "std_lib_facilities.h"
#include "Header1.h"

vector<int> binary_import(vector<int>& b)
{
	string iname;
	cout << "Type filename input: ";
	cin >> iname;

	ifstream ifs{ iname,ios_base::binary };
	if (!ifs) error("Cannot input filename ", iname);

	for (int x; ifs.read(as_bytes(x), sizeof(int));)
	{
		b.push_back(x);
	}

	return b;
}

void binary_export(const vector<int>& b)
{
	string oname;
	cout << "Type filename output: ";
	cin >> oname;

	ofstream ofs{ oname, ios_base::binary };

	for (int x : b)
	{
		ofs.write(as_bytes(x), sizeof(int));
	}
}

Input txt file:
La mia casa si trova in Calabria ed e' esattamente a Cosenza. Questo file sarà analizzato in una modalità
binaria attraverso l'importazione dei dati in quest'ultimo formato.

Output txt file:
La mia casa si trova in Calabria ed e' esattamente a Cosenza. Questo file sarà analizzato in una modalità
binaria attraverso l'importazione dei dati in quest'ultimo format

Notice chars o. are gone in output file.

[Peter87]

What I think happens is this:

An int is probably 4 bytes (it usually is) which means your program is reading and writing data in chunks of 4 bytes.

When the only thing left to be read from the file is "to." the read operation will fail because you are trying to read 4 bytes but there are only 3 bytes, so "to." is never added to the vector.

[leourb]

I thought something like that but I was not sure because I am dealing with binary I/O from few time.. In a real situation like that how could this problem be handled? Thanks!

[Peter87]

Use char instead of int.

[leourb]

Ok thanks!

[MiiNiPaa]

Also in real application you want to read data in larger chunks _{^{(and probably in another thread)}}:

std::vector<char> binary_import()
{
    std::string iname;
    std::cout << "Type filename input: ";
    std::cin >> iname;

    std::ifstream ifs {iname, std::ios::binary };
    if (!ifs) error("Cannot input filename ", iname);

    constexpr size_t buf_size = 64;
    char buffer[buf_size];

    std::vector<char> b;
    while (ifs.read(buffer, buf_size)){
        b.insert(b.end(), buffer, buffer + buf_size);
    }
    b.insert(b.end(), buffer, buffer + ifs.gcount());
    return b;
}

void binary_export(const std::vector<char>& b)
{    
    std::string oname;
    std::cout << "Type filename output: ";
    std::cin >> oname;

    std::ofstream ofs{oname, std::ios::binary };
    ofs.write(b.data(), b.size());
}

Note that I use gcount after loop to check if there and how many symbols read before eventual failure. You might use it to adapt your original program (however I have no ide what you would do with missing bytes)