UTF-8 Encoded std::wifstream support

utf8wifstream.cpp

#include <iostream>
#include <ifstream>
#include <string>

// Opens a file by path name. Assumes the file is UTF-8 encoded. If the file
// has a BOM, it'll be skipped so the first access to the file is positioned
// correctly.
std::wifstream open_utf8_with_maybe_bom(std::filesystem::path const& path)
{
    std::wifstream ss;
    ss.imbue(std::locale(".utf-8"));
    ss.open(path);

    if (ss.good() && (ss.peek() == 0xFEFF))
        (void)ss.get();

    return ss;
}

// Use notepad to create a file called "test-app.txt", and save it with the "UTF-8 with BOM" encoding

void do_test()
{
    auto stream = open_utf8_with_maybe_bom(std::filesystem::path("test-app.txt"));

    std::wstring t;
    while (std::getline(stream, t))
    {
        std::wcout << L"Line " << t << L" " << t.length() << std::endl;
    }
}

winrtDataJason.cpp

// Take the utf8wifstream.cpp, and add:

#include <sstream>
#include <winrt/Windows.Data.Json.h>

void read_json_file()
{
    auto stream = open_utf8_with_maybe_bom("test-app.json");
    std::wstringstream content;
    content << stream.rdbuf();
    auto obj = winrt::Windows::Data::Json::JsonObject::Parse(content.str());
    std::wcout << obj.ToString().c_str() << std::endl;
}

I suggest not using the Windows.Data.Json types - there are many other C++ JSON processing libraries out there that are much much better and easier to use.

Oh and because I love cryptic one-liners:

    auto obj = winrt::Windows::Data::Json::JsonObject::Parse((std::wstringstream{} << stream.rdbuf()).str());