open(const wchar_t *_Filename

QString qsFullFileName = QFileDialog::getOpenFileName(...);

if(!qsFullFileName.isEmpty())
        {
            //---
            std::ifstream ifs;

            ifs.open(qsFullFileName.toStdWString());

std::wstring QString::toStdWString() const

Returns a std::wstring object with the data contained in this QString. The std::wstring is encoded in utf16 on platforms where wchar_t is 2 bytes wide (e.g. windows) and in ucs4 on platforms where wchar_t is 4 bytes wide (most Unix systems).

__>QString qsFullFileName = QFileDialog::getOpenFileName(...);

__>if(!qsFullFileName.isEmpty())
__>        {
__>            //---
__>            std::ifstream ifs;

__>            ifs.open(qsFullFileName.toStdWString());
__>

QString qsFullFileName;

// Если исходный файл в кодировке: utf-8
qsFullFileName = QString::fromUtf8(R"(d:\WORK\!!!!!статья — блабла\programma\projs\conception\file)");
qsFullFileName = QTextCodec::codecForName("UTF8")->toUnicode(R"(d:\WORK\!!!!!статья — блабла\programma\projs\conception\file)");

// Если исходный файл в кодировке: Windows-1251
qsFullFileName = QTextCodec::codecForName("CP1251")->toUnicode(R"(d:\WORK\!!!!!статья — блабла\programma\projs\conception\file)");

std::ifstream ifs;
ifs.open(qsFullFileName.toLocal8Bit());

// Если код исполняется на ОС Windows (запуск из explorer'а, IDE)
ifs.open(QTextCodec::codecForName("CP1251")->fromUnicode(qsFullFileName));

// Если код исполняется на ОС Windows (запуск из CMD)
ifs.open(QTextCodec::codecForName("IBM866")->fromUnicode(qsFullFileName));

std::cout << "open = " << std::boolalpha << ifs.is_open() << std::endl;

"The width of wchar_t is compiler-specific and can be as small as 8 bits. Consequently, programs that need to be portable across any C or C++ compiler should not use wchar_t for storing Unicode text. The wchar_t type is intended for storing compiler-defined wide characters, which may be Unicode characters in some compilers."

QString filename(QString::fromUtf8("файл.txt"));
QFile file(filename);
if (file.open(QIODevice::ReadWrite))
{
    // ...
}

B>>QString filename(QString::fromUtf8("файл.txt"));
B>>QFile file(filename);
B>>if (file.open(QIODevice::ReadWrite))
B>>{
B>>    // ...
B>>}
B>>

std::ifstream f;
f.exceptions(std::ios_base::failbit | std::ios_base::badbit);
try
{
    f.open("some_file.txt");
}
catch (const std::exception& ex)
{
    std::cerr << ex.what() << std::endl;
}

21.5 Null-terminated sequence utilities [c.strings]

14 The functions strerror and strtok are not required to avoid data races (17.6.5.9).