Qt5 convert QString into char [] or char *

yczo

Hello, I googled a lot over that theme, all deprecated or do not work

QString hello = "Hello World"; ---> to char *cHello or to char cHello[30]

How to convert in Qt5 to a standard c++ char array?

i tried for(int i = 0; ;i++) cHello[i] = hello.at(i); .... and much more, but without sucess

Someone kind enough to help? please help :-)

thanks in advance. greetings

Aggs

@yczo hello.ToStdString().c_str()

yczo

Thank you very much for answer, but i think that this is deprecated method. :-(
When I run
char *cHello = hello.ToStdString().c_str();

get the next error:

error: C2039: 'ToStdString' : is not a member of 'QString'

? Offline

Just a typo. It's std::string QString::toStdString() const.

sneubert

hi yczo,
try hello.toStdString().c_str();
mind the small letter

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

yczo

but... there is not a way to direct obtain a char array instead of a string? the question was over an char array hehee ;-)

char *cHola =

Thank you very much (I appreciate the kindness)...

sneubert

you are right, the pointer you get is const, but you can do something like

char cHola[512] = {0};
std::copy(hello.toStdString().begin(),hello.toStdString().end(),cHola);

but remind that there´s no boundary check on cHola and you get nonsens if it´s not a basic_string<char>

mrjj

@yczo
hi
Nope
QString dont convert directly to char *.

But can I ask why u need char * ?

QString class can do anything u can do with char * and in better and more safe way.

yczo

Hello and thank you; I need "char *hola" or "char hola[maxSize]" for send simply chars to serial port through Windows handler

Greetings

sneubert

so the answer is already there, something like
WriteFile(yourComHandle, hello.toStdString().c_str(), hello.length(), &dw_bytesWritten, NULL)
should do the job

kshegunov

@yczo said:

I need "char *hola" or "char hola[maxSize]" for send simply chars to serial port through Windows handler

You're better of using QSerialPort (which accepts QByteArray) and respecting the string's encoding. Also referencing temporaries can be inconspicuously dangerous in some cases. Consider this (modified from @sneubert's example):

char * string = hello.toStdString().c_str(); // Now we get a dangling pointer to a location we don't own!
WriteFile(yourComHandle, string, hello.length(), &dw_bytesWritten, NULL); // Might work, depending on the compiler, might get a segfault

How about this, doesn't it look better:

QSerialPort port;
// ... init and so on ...

QByteArray data = hello.toLatin1(); // Enforce latin1 encoding (or utf8, or local 8-bit or whatever your device is expecting)
port.write(data);
port.waitForBytesWritten(1000); // Only for illustration, you can (and should) use the async API
// ... and so on ...

Or, if you really insist on using char *, then enforce the encoding to a byte-array and then get the char pointer from there:

QByteArray string = hello.toLatin1();
char * strdata = string.data(); // This pointer is valid during the lifetime of the QByteArray instance (provided the byte array is not changed in the meantime)