How to convert QString to std::string?

Question

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?

Answer 1

You can use:

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

It internally uses QString::toUtf8() function to create std::string, so it's Unicode safe as well. Here's reference documentation for QString.

Answer 2

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

Answer 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.

Answer 4

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

However, if you're using Qt:

QTextStream out(stdout);
out << qstr;

Answer 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();
}

Answer 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.

Answer 7

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

Answer 8

You can use this;

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

Answer 9

There is also the option to use qPrintable or qUtf8Printable

E.g.:

#include <QString>
#include <iostream>

int main()
{
    QString myString = "Hello World";

    // Using qPrintable
    std::cout << "qPrintable: " << qPrintable(myString) << std::endl;

    // Using qUtf8Printable
    std::cout << "qUtf8Printable: " << qUtf8Printable(myString) << std::endl;

    return 0;
}

Answer 10

 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();

Answer 11

HA~I finally find the answer which I can run! Share to you now~

QString qStr = "Hello world";
QByteArray qByteArray = qStr.toUtf8();
char* cStr = qByteArray.data();
const char* test = cStr;
qDebug()<<test<<endl;

Answer 12

Try this:

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