How to convert QString to std::string?

问题

I am trying to do something like this:

QString string;
// do things...
std::cout << string << std::endl;

but the code doesn\'t compile. How to output the content of qstring into the console (e.g. for debugging purposes or other reasons)? How to convert QString to std::string?

回答1:

One of the things you should remember when converting QString to std::string is the fact that QString is UTF-16 encoded while std::string... May have any encodings.

So the best would be either:

QString qs;

// Either this if you use UTF-8 anywhere
std::string utf8_text = qs.toUtf8().constData();

// or this if you're on Windows :-)
std::string current_locale_text = qs.toLocal8Bit().constData();

The suggested (accepted) method may work if you specify codec.

See: http://doc.qt.io/qt-5/qstring.html#toLatin1

回答2:

You can use:

QString qs;
// do things
std::cout << qs.toStdString() << std::endl;

Here's reference documentation for QString.

回答3:

If your ultimate aim is to get debugging messages to the console, you can use qDebug().

You can use like,

qDebug()<<string; which will print the contents to the console.

This way is better than converting it into std::string just for the sake of debugging messages.

回答4:

QString qstr;
std::string str = qstr.toStdString();

However, if you're using Qt:

QTextStream out(stdout);
out << qstr;

回答5:

Best thing to do would be to overload operator<< yourself, so that QString can be passed as a type to any library expecting an output-able type.

std::ostream& operator<<(std::ostream& str, const QString& string) {
    return str << string.toStdString();
}

回答6:

An alternative to the proposed:

QString qs;
std::string current_locale_text = qs.toLocal8Bit().constData();

could be:

QString qs;
std::string current_locale_text = qPrintable(qs);

See qPrintable documentation, a macro delivering a const char * from QtGlobal.

回答7:

The simplest way would be QString::toStdString().

回答8:

You can use this;

QString data;
data.toStdString().c_str();

回答9:

 QString data;
   data.toStdString().c_str();

could even throw exception on VS2017 compiler in xstring

 ~basic_string() _NOEXCEPT
        {   // destroy the string
        _Tidy_deallocate();
        }

the right way ( secure - no exception) is how is explained above from Artyom

 QString qs;

    // Either this if you use UTF-8 anywhere
    std::string utf8_text = qs.toUtf8().constData();

    // or this if you're on Windows :-)
    std::string current_locale_text = qs.toLocal8Bit().constData();

回答10:

Try this:

#include <QDebug>
QString string;
// do things...
qDebug() << "right" << string << std::endl;

来源：https://stackoverflow.com/questions/4214369/how-to-convert-qstring-to-stdstring

标签

c++

type-conversion

qstring