4

I have a very basic question here. I tried googling for a while, because there are a lot of similar questions but none of the solutions worked for me.

here is a code snippet that shows the problem:

QString test = "hello";
unsigned char* test1 = (unsigned char*) test.data();
unsigned char test2[10];
memcpy(test2,test1,test.size());
std::cout<<test2;

I try to fit the QString into the unsigned char array but the output I get is always just 'h'.

Can anyone tell me what is going wrong here?

samoncode
  • 466
  • 2
  • 7
  • 23
  • 2
    Note that a QChar is a 16-bit thing, storing a Unicode codepoint. For an 'h' (any US-ASCII) the high order byte will be 0. This explains why your output only shows 'h'. – laune Feb 18 '14 at 15:35
  • @laune Thank you. I didn't knew that. – samoncode Feb 18 '14 at 19:50

3 Answers3

8

Problem is in that QString.data() returns a QChar* but you want const char*

QString test = "hello";
unsigned char test2[10];
memcpy( test2, test.toStdString().c_str() ,test.size());
test2[5] = 0;
qDebug() << (char*)test2;
             ^^^
            this is necessary becuase otherwise
            just address is printed, i.e. @0x7fff8d2d0b20

The assignment 

unsigned char* test1 = (unsigned char*) test.data();

and trying to copy

unsigned char test2[10];
memcpy(test2,test1,test.size());

is wrong, because QChar is 16 bit entity and as such trying to copy it will terminate because of 0 byte just after 'h'.

4pie0
  • 29,204
  • 9
  • 82
  • 118
3

In the second line you're trying to cast QChar* to (unsigned char*) which is completely wrong.

Try this:

QString test = "hello";
QByteArray ba = test.toLocal8Bit();
unsigned char *res = (unsigned char *)strdup(ba.constData());
std::cout << res << std::endl;
hank
  • 9,553
  • 3
  • 35
  • 50
0

If you want to use Russian sims in the text that is written in the QString, then use this method.

unsigned char* temp;
QString name = "М102";
QByteArray ba = name.toUtf8();
temp = (unsigned char*)ba.data();
Андрей Демичев
  • 1