How to convert QString to std::string?
-
26-09-2019 - |
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
?
Solution
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.
OTHER TIPS
You can use:
QString qs;
// do things
std::cout << qs.toStdString() << std::endl;
Here's reference documentation for QString
.
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.
QString qstr;
std::string str = qstr.toStdString();
However, if you're using Qt:
QTextStream out(stdout);
out << qstr;
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();
}
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.
The simplest way would be QString::toStdString()
.
You can use this;
QString data;
data.toStdString().c_str();
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();
Try this:
#include <QDebug>
QString string;
// do things...
qDebug() << "right" << string << std::endl;