Assigning quint16_t to QByteArray while sending serial data frame from PC to device

[d_stranz]

I have twice edited your posts in this thread to add CODE tags to your source code listings. Please use them for your future posts. See my signature below if you don't know how.

My question is How can I make sure irrespective of value in the "len" and "checksum", I want to allocate 2bytes for each fields in the serial frame.

I told you in my previous answer: Do not append "sizeof( hdr )", append a quint16_t variable which contains the sizeof( hdr ) value. sizeof() will return the smallest representation of the number of bytes in the argument (in your case 4 for "hdr"), which fits into a single byte, so a single byte is what gets appended. If you want 2 bytes to be appended, then you have to append a 2 byte variable.

[ChrisW67]

There is no QByteArray function to append() anything other than chars (bytes).

The sizeof(hdr) is a size_t with the value 4 (probably). size_t is variously defined, but must be at least 16-bits long and often an unsigned 32 or 64-bit integer.
At line 27 you append a single char with the value stored in the size_t (it is an implied cast). One byte in the array is what you get. As a length value it will be broken if the hdr ever exceeds 255 bytes.

If you want to write a multi-byte integer using only QByteArray then you need to code breaking it into bytes and appending them in the correct order (whichever way round that is). Something like:

size_t hdrlen = sizeof(hdr);
tx_msg->append(hdrlen & 0xff)
hdrlen = hdrlen >> 8;
tx_msg->append(hdrlen & 0xff)

size_t hdrlen = sizeof(hdr);
tx_msg->append(hdrlen & 0xff)
hdrlen = hdrlen >> 8;
tx_msg->append(hdrlen & 0xff)

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or you can go this way (making the result platform architecture sensitive... your other code already is):

uint16_t hdrlen = sizeof(hdr);
tx_msg->append((char *) &hdrlen, sizeof(hdrlen));

uint16_t hdrlen = sizeof(hdr);
tx_msg->append((char *) &hdrlen, sizeof(hdrlen));

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You could also (carefully) use QDataStream.

[anita.niharika@gmail.com]

There is no QByteArray function to append() anything other than chars (bytes).

The sizeof(hdr) is a size_t with the value 4 (probably). size_t is variously defined, but must be at least 16-bits long and often an unsigned 32 or 64-bit integer.
At line 27 you append a single char with the value stored in the size_t (it is an implied cast). One byte in the array is what you get. As a length value it will be broken if the hdr ever exceeds 255 bytes.

If you want to write a multi-byte integer using only QByteArray then you need to code breaking it into bytes and appending them in the correct order (whichever way round that is). Something like:

size_t hdrlen = sizeof(hdr);
tx_msg->append(hdrlen & 0xff)
hdrlen = hdrlen >> 8;
tx_msg->append(hdrlen & 0xff)

size_t hdrlen = sizeof(hdr);
tx_msg->append(hdrlen & 0xff)
hdrlen = hdrlen >> 8;
tx_msg->append(hdrlen & 0xff)

To copy to clipboard, switch view to plain text mode 

or you can go this way (making the result platform architecture sensitive... your other code already is):

uint16_t hdrlen = sizeof(hdr);
tx_msg->append((char *) &hdrlen, sizeof(hdrlen));

uint16_t hdrlen = sizeof(hdr);
tx_msg->append((char *) &hdrlen, sizeof(hdrlen));

To copy to clipboard, switch view to plain text mode 

You could also (carefully) use QDataStream.

Thanks Chris. I could figure out the first approach mentioned above.