Найти UTF-16 строку в бинарном файле

void scrambleWide(const char *filename, const char key) 
{
    std::wfstream ifs(filename, ios::binary|ios::out|ios::in);
    if(!ifs.is_open())
    {
        printf("Unable to open file in wide mode...\n");
        return;
    }
 
    ifs.imbue(std::locale(ifs.getloc(), new std::codecvt_utf8<wchar_t>));
 
    std::wstring str((std::istreambuf_iterator<wchar_t>(ifs)), std::istreambuf_iterator<wchar_t>());
 
    std::wsmatch matches;
    std::wregex rgx (L"(START_MARK)(.*?)(END_MARK)");
    std::wstring fullMatch, stringMatch;
    size_t appendSize;
 
    while (std::regex_search (str,matches,rgx)) {
        printf("Found match: %s at position: %d...", matches[2].str().c_str(), matches.position(2));
 
        fullMatch = matches[0].str(); 
        stringMatch = matches[2].str();
        appendSize = fullMatch.size() - stringMatch.size(); 
 
        stringMatch.append(appendSize, L'\0');
 
        ifs.seekp(matches.position(0));
        ifs.write(stringMatch.c_str(), stringMatch.size());
 
        printf("replaced\n");
 
        str = matches.suffix().str();
    }
    ifs.close();
}

bool scramble(const char *filename, const char key) 
{
    printf("Running in narrow char mode...\n");
    std::fstream ifs(filename, ios::binary|ios::out|ios::in);
    std::string str((std::istreambuf_iterator<char>(ifs)), std::istreambuf_iterator<char>());
 
    std::smatch matches;
    std::regex rgx ("(START_MARK)(.*?)(END_MARK)");
    std::string fullMatch, stringMatch;
    size_t appendSize;
 
    bool somethingFound = false;
 
    if (std::regex_search (str,matches,rgx)) {
        somethingFound = true;
        fullMatch = matches[0].str(); 
        stringMatch = matches[2].str();
        appendSize = fullMatch.size() - stringMatch.size(); 
 
        for(size_t i = 0; i < stringMatch.size(); i++)
        {
            stringMatch[i] ^= key;
        }
 
        stringMatch.append(appendSize, '\0');
 
        printf("Found string: %s at position: %d\n", stringMatch.c_str(), matches.position(0));
 
        ifs.seekp(matches.position(0));
        ifs.write(stringMatch.c_str(), stringMatch.size());
    }
 
    ifs.close();
 
    return somethingFound;
};

ifs.imbue(std::locale(ifs.getloc(), new std::codecvt_utf16<wchar_t>));

for(size_t i = 0; i < stringMatch.size(); i++)
        {
            stringMatch[i] ^= key;
        }

std::wstring str (L"bla-bla-bla MARK_BEGINsomewidestringMARK_END bla-bla");