QByteArray data format explanation

I am confused about QByteArray data. Can someone please explain the below scenario for me. enter image description here

Here data type for each array index is char. I understand some of those values. Like 74 'J' I understand the first one is ASCII and second one is the corresponding character. But what is the meaning of -1 '\\377'

Also what does the below gui means?? I sent the QByteArray of above to a function which takes the QByteArray as unsigned char* source. The below gui is showing the value of that source. enter image description here

The main confusing part is the first line's value 0x87089e8 "\377\330\377\340"

Solution

char in C/C++ is a signed 1-byte integer. This GUI is simply expressing that value as a signed decimal number, and the equivalent ASCII character.

You're asking about the byte value -1, which can be interpretted in the following ways:

Binary     11111111
Octal      0377
Hex        0xFF
Decimal    -1    (Signed)
           255   (Unsigned)

ASCII      \377
           \xFF

Note that there isn't a standard printable ASCII character for 255, which is why they show it like they do.

Another Example:

Binary     01001010
Octal      0112
Hex        0x4A
Decimal    74    (Signed)
           74   (Unsigned)
ASCII      'J'