[ACCEPTED]-Converting QString to char*-qt4

Accepted answer
Score: 52

See here at How can I convert a QString to char* and vice versa?

In order to convert a QString to a char*, then 16 you first need to get a latin1 representation 15 of the string by calling toLatin1() on 14 it which will return a QByteArray. Then 13 call data() on the QByteArray to get a 12 pointer to the data stored in the byte 11 array. See the documentation:

https://doc.qt.io/qt-5/qstring.html#toLatin1 https://doc.qt.io/qt-5/qbytearray.html#data

See the 10 following example for a demonstration:

int main(int argc, char **argv)
 QApplication app(argc, argv);
  QString str1 = "Test";
  QByteArray ba = str1.toLatin1();
  const char *c_str2 = ba.data();
  printf("str2: %s", c_str2);
  return app.exec();

Note 9 that it is necessary to store the bytearray 8 before you call data() on it, a call like 7 the following

const char *c_str2 = str2.toLatin1().data();

will make the application crash 6 as the QByteArray has not been stored 5 and hence no longer exists

To convert a 4 char* to a QString you can use the QString 3 constructor that takes a QLatin1String, e.g:

QString string = QString(QLatin1String(c_str2)) ;

See 2 the documentation:


Of course, I discovered 1 there is another way from this previous SO answer:

QString qs;

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

// or this if you on Windows :-)
std::string current_locale_text = qs.toLocal8Bit().constData();
Score: 3

You could use QFile rather than std::fstream.

QFile           file(qString);

Alternatively 14 convert the QString into a char* as follows:

std::ifstream   file(qString.toLatin1().data());

The 13 QString is in UTF-16 so it is converted toLatin1() here 12 but QString has a couple of different conversions 11 including toUtf8() (check your file-system 10 it may use UTF-8).

As noted by @0A0D above: don't store 9 the char* in a variable without also getting 8 a local copy of the QByteArray.

char const*      fileName = qString.toLatin1().data();
std::ifstream    file(fileName);  // fileName not valid here.

This is because 7 toLatin1() returns an object of QByteArray. As 6 it is not actually bound to a variable it 5 is a temporary that is destroyed at the 4 end of the expression. Thus the call to 3 data() here returns a pointer to an internal 2 structure that no longer exists after the 1 ';'.

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