Question

I need to add to a QByteArray 4 bytes, as frame. (struct ([4 bytes][message]))

I do:

 QByteArray byteArray;
 QByteArray byteArray2(man.SerializeAsString().c_str(), man.ByteSize()); // 31 byte
 qDebug()<<byteArray.size()<<"size"; // 0 bytes
 byteArray.resize(3); 
 qDebug()<<byteArray.size()<<"size"; // 3, ok
 byteArray.append(man.ByteSize()); 
 qDebug()<<byteArray.size()<<"size"; // 4
 byteArray2.prepend(byteArray);     
 qDebug()<<byteArray2.size()<<"size"; // return 35, ok
 qDebug()<<(byteArray2); // not print my message

Sorry for my english.

Answer 1

You’re trying to print a string that (should) start with \0 characters (binary zero). qDebug() will most likely not print anything at all – \0 is a string terminator.

But there’s a bug in your code, you should be doing:

 byteArray.fill(0, 3);

instead of the resize call, otherwise you’ll get random data in the first bytes.