QString use .c_str()?

[therock1987]

Qt 4.5 QString have a way to output a null terminaded string ( QString.cstr() )

[wysota]

QString::toLatin1(), QString::toLocal8Bit(), QString::toAscii() and then QByteArray::constData().

[jonthom]

Could also do this:

#include <string>
 
char * c_string = QString().toStdString().c_str();

#include <string>

char * c_string = QString().toStdString().c_str();

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[jonthom]

Could also do this:

#include <string>
 
char * c_string = QString().toStdString().c_str();

#include <string>

char * c_string = QString().toStdString().c_str();

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edit*

const char * c_string = QString().toStdString().c_str();

const char * c_string = QString().toStdString().c_str();

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[wysota]

This code is incorrect. It will segfault in many situations.

[jonthom]

how so? I use this method often to convert QStrings into c-strings and its never seg faulted. In what situtation does it seg fault?

[jonthom]

maybe the confusion here is my semi pseudo code:

QString str = "Some string";
const char * c_string = str.toStdString().c_str();

QString str = "Some string";
const char * c_string = str.toStdString().c_str();

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not

const char * c_string = QString().toStdString().c_str();

const char * c_string = QString().toStdString().c_str();

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I agree putting the latter line into code would probably segfault or return NULL to the pointer. Sorry for the confusion.

[wysota]

No, that's still wrong. The whole concept of doing what you are doing is wrong.

[Timoteo]

Is this the whole "intermediate references smell like poo" thing?

[jonthom]

Well could you explain why you think that? I dont see how its any different from converting to a QBtyeArray and pulling the char * out of it.

[wysota]

Well could you explain why you think that? I dont see how its any different from converting to a QBtyeArray and pulling the char * out of it.

Well, this is wrong too of course:

QString str = "xxx";
const char *cstr = str.toAscii().constData();

QString str = "xxx";
const char *cstr = str.toAscii().constData();

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This is much better although might still be wrong in some cases:

QString str = "xxx";
QByteArray ba = str.toAscii();
const char *cstr = ba.constData();

QString str = "xxx";
QByteArray ba = str.toAscii();
const char *cstr = ba.constData();

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This is ok:

QString str = "xxx";
QByteArray ba = str.toAscii();
const char *cstr = strcpy(ba.constData());

QString str = "xxx";
QByteArray ba = str.toAscii();
const char *cstr = strcpy(ba.constData());

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So is this:

QString str = "xxx";
QByteArray ba = str.toAscii();
someCallThatNeedsACStr(ba.constData());

QString str = "xxx";
QByteArray ba = str.toAscii();
someCallThatNeedsACStr(ba.constData());

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[jonthom]

Ok i see what you mean now. Yes, if you want a deep copy that you can manipulate safely strcpy() is the way to go. Other than that, this method is effectively the same as using a std::string as the medium. My code was intended for use as an argument to a function that wants a c-str. Also, getting the shallow copy isnt necessarily "wrong" it just depends on what you intend to do with it.