Myujth

I have a qTextEdit that I grab the text from (QString) and convert to a char* with this code:

QString msgQText = ui->textMsg->toPlainText();
size_t textSize = (size_t)msgQText.size();

if (textSize > 139) 
 textSize = 139;


unsigned char * msgText = (unsigned char *)malloc(textSize);

memcpy(msgText, msgQText.toLocal8Bit().data(), textSize);

msgText[textSize] = '';

if (textSize > 0) 
 Msg * newTextMsg = new Msg;
 newTextMsg->type = 1; // text message type
 newTextMsg->bitrate = 0;
 newTextMsg->samplerate = 0;
 newTextMsg->bufSize = (int)textSize;
 newTextMsg->len = 0;
 newTextMsg->buf = (char *)malloc(textSize);
 memcpy((char *)newTextMsg->buf, (char *)msgText, textSize);

 lPushToEnd(sendMsgList, newTextMsg, sizeof(Msg));

 ui->sendRecList->addItem((char *)newTextMsg->buf);

 ui->textMsg->clear();

I put the text into a qListBox, but it shows up like

However, the character array, if I print it out, does not have the extra characters.

I have tried checking the "compile using UTF-8" option, but it doesn't make a difference.

Also, I send the text using RS232, and the receiver side also displays the extra characters.

The receiver code is here:

m_serial->waitForReadyRead(200);
const QByteArray data = m_serial->readAll();
if (data.size() > 0) 
 qDebug() << "New serial data: " << data;

 QString str = QString(data);
 if (str.contains("0x6F8C32E90A")) 
 qDebug() << "TEST SUCCESSFUL!";
 

 return data.data();
 else 
 return NULL;

There is a difference between the size of a QString and the size of the QByteArray returned by toLocal8Bit(). A QString contains unicode text stored as UTF-16, while a QByteArray is "just" a char.

A QByteArray is null-terminated, so you do not need to add it manually.

As @GM pointed out: msgText[textSize] = ''; is undefined behavior. You are writing to the textSize + 1 position of the msgText array.
This position may be owned by something else and may be overwritten, so you end up with a non null terminated string.

This should work:

QByteArray bytes = msgQText.toLocal8Bit();
size_t textSize = (size_t)bytes.size() + 1; // Add 1 for the final ''
unsigned char * msgText = (unsigned char *) malloc(textSize);
memcpy(msgText, bytes.constData(), textSize);

Additional tips:

• Prefer using const functions on Qt types that are copy-on-write, e.g. use QBytearray::constData() instead of QByteArray::data(). The non-const functions can cause a deep-copy of the object.




• Do not use malloc() and other C-style functions if possible. Here you could do:
  unsigned char * msgText = new unsigned char[textSize]; and later delete msgText;.




• Prefer using C++ casts (static_cast, reinterpret_cast, etc.) instead of C-style casts.



• You are making 2 copies of the text (2 calls to memcpy), given your code only 1 seem to be enough.