QByteArray sum

[high_flyer]

A byte is nothing more than a group of bits that define a unit of digital data.
It is true that de facto today 8 bit bytes are the common case, but there is no standard defining it.
The size of a byte is hardware define.

In short, you want the values in ints that are 8 bits wide, commonly represented by 'char' (or unsigned char).

The requirement makes little sense.
Is it guaranteed that the count of the items in your QByteArray and the sum of their values really is not larger than 255??
I strongly doubt that.
And if it is guaranteed, than the type in which you store your sum can be any larger integer type, it wont matter - the sum will not exceed 255

Maybe if you'd explain what is the problem you are trying to solve with summing your QByteArray we could help you to come to the correct solution.

[FalloutST]

for(i=0; bla bla) {
bytearray[0] = bytearray[0] + byteadday2[i];
}

that is the way I did it,
both of us, I guess, expect value 256 in byte as 0, overflow will do it's work
11111111 = 255
100000000 = 256

AVR chip work with bytes and it is sensitive to push it to 16.
I am already using 68% of RAM it have.
It count sum of received data bytes, but c++ do so with "сrutch" at the top of the post.
I guess there must be other... "true" way to do so...

[d_stranz]

It sounds like you are confused in your requirements. Do you want to:

- count the number of bytes in the byte array
- compute the sum of the byte values in the array
- do something else?

In the first two cases, either of these could be greater than 255, even if the value of any byte in the array has the range 0 <= byte <= 255.

The fake code you show in your last post won't compile and doesn't even make a lot of sense. If you want real help on this forum, have some respect for the people who are willing to help you by at least posting a piece of your actual code so we can try to understand what you might be doing wrong.

[FalloutST]

1) second
2)

qDebug() << "data3=" << data;
    for (int i = 0; i < sp_dataLength; i++) {
       bytearray[0] = bytearray[0] + sp_ar_dataToSend[i]; // QByteArray sp_ar_dataToSend;
    }
    data.append((const char*)(bytearray), sizeof(char));

qDebug() << "data3=" << data;
    for (int i = 0; i < sp_dataLength; i++) {
       bytearray[0] = bytearray[0] + sp_ar_dataToSend[i]; // QByteArray sp_ar_dataToSend;
    }
    data.append((const char*)(bytearray), sizeof(char));

To copy to clipboard, switch view to plain text mode 

compiled, work fine
not tested with overflow yet

[high_flyer]

compiled, work fine

Well, depends what you define as "works".
If all your bytes contain the value 1, then sp_ar_dataToSend is not allowed to have more than 255 elements.
In such a case any larger array will give you false sum.
Another case is when you array holds bytes that are considerably larger than 1, which in any real work situation is sure to be.
Lets say you have 3 bytes in the array each with the value of 100.
In that case your sum is definitely wrong.
Also note I totally neglected the fact you always add the last sum to the new value, this makes your sum calculation probably wrong all the time since it limits the values you can add even more.
So the code will run since it is syntactically correct (hence you could say "work"), but the sum most certainly will be false.

May we ask what is the purpose of this sum?
Are you trying to make a checksum so that the receiver can be certain the data is correct or maybe so that the receiver can allocate enough buffer memory?
(if this is a checksum, there are some nice examples on the Internet maybe the AVR lib has a function for it as well)

I am already using 68% of RAM it have.

It sounds to me that because you want your 0 array item to hold the sum of bytes in the array, you are limited to use an 8bit byte to store the sum.
Why don't you send a struct instead of the array that will hold both informations:

sturct dataPacket {
long int sum;
QByteArray data;
};

sturct dataPacket {
long int sum;
QByteArray data;
};

To copy to clipboard, switch view to plain text mode 

This way you are not limited to the 8bit byte as a holder for your sum.
Of course you should know what the largest sum you can have (0xFF * size of array) and make sure its less than what the long int can hold on your AVR.

[FalloutST]

AVR

for (int i = 1; i < sp_dataLength; i++) {
       sum += sp_recievedData[i];
   }

for (int i = 1; i < sp_dataLength; i++) {
       sum += sp_recievedData[i];
   }

To copy to clipboard, switch view to plain text mode 

Qt

for (int i = 0; i < sp_dataLength; i++) {
       bytearray[0] = bytearray[0] + sp_ar_dataToSend[i];
    }

for (int i = 0; i < sp_dataLength; i++) {
       bytearray[0] = bytearray[0] + sp_ar_dataToSend[i];
    }

To copy to clipboard, switch view to plain text mode 

output
sp_recievedData[i] : 1, 10, 215, 35, 60
result sum: 65
result bytearray[0] : 65

bytearray[0] - is QByteArray same as dataToSend

1+10+215+35+60 = 321 - 256 = 65

May I ask you?
If so: why should I count it in integer if it is loss prevention protocol?

My question is replacement bytearray[0] by other variable, in QT, to operate BYTE. CHAR crush....

I can't say it other "clear" way.