Qt QByteArray无符号数据类型

Question

I need to send data over rs232,but I'm facing a problem.
When I send byte representing integer over 128, it looks like QByteArray changes the content I feed it:

uchar uc_array[]={0x41,0xAA}; //65 170
QByteArray qb_array = QByteArray();
qb_array.append(uc_array[0]);
qb_array.append(uc_array[1]);
cout<<(uint)qb_array[0]<<endl //65
cout<<(uint)qb_array[1]<<endl //4294967210

Why

 cout<<(uint)qb_array[1]<<endl

doesn't print 170, but 4294967210 instead ?

Answer 1

Here is my explanation of why you print 4294967210 instead of 170, which is your original question:

1. qb_array[1] returns a signed char type with 0xAA value
2. When you cast a signed char to uint type:
   • the value is first promoted to int type, keeping the sign: it becomes 0xFFFFFFAA
   • then it is interpreted as unsigned, so 4294967210 in decimal format.
3. Printing this value in decimal format gives 4294967210.