About QByteArray

[taku-s]

Hello, everyone.
I'm using Qt 5.15.1 + MSVC2019 32bit.
I have a few questions.
When I compile the following code

There's a warning on line 22.
C4309: 'conversion': truncation of constant value

I think the BYTE range is 256, why?

There is an error on line 23.
call to member function 'append' is ambiguous
candidate function

On line 15, it's not a problem, so why is it?

Best regards, thank you.

1	#include <Windows.h>
2	
3	void MainWindow::on_pushButton_clicked()
4	{
5	    BYTE data[5];
6	    data[0] = 0x08;
7	    data[1] = 0x86;
8	    data[2] = 0x00;
9	    data[3] = 0x41;
10	    data[4] = 0x53;
11
12	    QByteArray Byt;
13
14	    for(int i=0; i<5; i++){
15	        Byt.append(data[i]);
16	    }
17
18	    ui->lineEdit->setText(Byt.toHex(' '));
19
20	    Byt.clear();
21	    Byt.append(0x08);
22	    Byt.append(0x86);
23	    Byt.append(0x00);						call to member function 'append' in ambiguous
24	    Byt.append(0x41);
25	    Byt.append(0x53);
26
27	    ui->lineEdit_2->setText(Byt.toHex(' '));
28	}

[JonB]

@taku-s said in About QByteArray:
BYTE is probably unsigned char, or similar. In lines 21--25 you are passing literal numbers, which are ints.

The warning on #22 is doubtless because Byt.append(0x86); has its top bit set/negative value? At a guess, the "ambiguous" Byt.append(0x00); is because with value 0 it could be a pointer and it doesn't know between QByteArray &QByteArray::append(char ch) and QByteArray &QByteArray::append(const char *str)?

Make your constant values chars, like char(0x08) or unsigned char(0x08), or as character constants like '\x08'.

[taku-s]

Thank you for explaining this in detail.
I've managed to understand it.