How to split QbyteArray most efficiently?

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I want to partition a QByteArray message efficiently, insert gap after 1 byte.
QByteArray contain 8byte data.

EX:
QByteArray qba = AABBCCDDEEFF9988

I want to write this into txt file in the following format.

AA BB CC DD EE FF 99 88

Any help would be great =)

Posted 17-Dec-15 1:24am

XamBEE

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Comments

Andreas Gieriet 17-Dec-15 7:36am

What is the problem? You do not know how to convert a byte value into a hex text representation? or how to add a space?
By what means "efficient"? Easy to write/read as a programmer? Quick execution? Little memory usage? ...?
Where does the text go to? Into an std::string or into a std::ostream, or anything else?
Cheers
Andi

XamBEE 17-Dec-15 7:43am

how to add space ?
yes i want to add spaces

To make is easy to read as programmer

Andreas Gieriet 17-Dec-15 7:47am

Pseudo code:

f = open file
foreach byte in bytearray do
t = convert byte to hex
write t to f
write space to f
end foreach
close f

What of the above mentioned pseudo code causes troubles?
Cheers
Andi

2 solutions

Solution 2

To write a char (i.e. a "byte") as upper case hex string into an output stream, you might do the following:

C++

#include <iostream>
#include <iomanip>
...
ostream& toHex(ostream& output, unsigned char byte) {
    return output << hex
                  << uppercase
                  << setw(2)
                  << setfill('0')
                  << int(byte);
}

Usage:

C++

for(int i = 0; i < n; i++) {
    cout << toHex(cout, bytes[i]) << " ";
}
cout << endl;

Cheers
Andi

Posted 17-Dec-15 7:50am

Andreas Gieriet

Updated 17-Dec-15 8:11am

v3

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Jochen Arndt · Accepted Answer · 2015-12-17T01:46:00

Solution 1

This can be best done using printf formatting:

FILE *f = fopen("test.txt", "w");
for (int i = 0; i < qba.size(); i++)
{
    if (i)
        fprintf(f, " ");
    fprintf(f, "%02X", (unsigned char)qba.at(i));
}
fprintf(f, "\n");
fclose(f);

If your file is already opened by another method than fopen, check if you can get a FILE pointer for the opened file or use sprintf with a local buffer and write that to the file.

[UPDATE]
For an existing QTextStream like from the comment it can be:

mylog << " " << currtTimeStump "," << MsgDLC << "," << frameID << ",";
for (int i = 0; i < qba.size(); i++)
{
    char dataByte[4];
    sprintf(dataByte, " %02X", (unsigned char)qba.at(i));
    mylog << dataByte; 
}
mylog << '\n';

Posted 17-Dec-15 1:46am

Jochen Arndt

Updated 17-Dec-15 4:39am

v4

Comments

XamBEE 17-Dec-15 7:53am

I am not reading it from the file. Actually i want to write into the file with spaces. so before writing into the file QByteArray qba = AABBCCDDEEFF9988.
here is one line of my txt file.
13:33:44:095, 10826196, 1, 0x701, 7faabbccddeeff66
I want to write something like
13:33:44:095, 10826196, 1, 0x701, 7f aa bb cc dd ee ff 66

Jochen Arndt 17-Dec-15 7:59am

That is what my solution does:
- It opens the file test.txt for writing
- It loops through the number of bytes
-- It prints a space to the file if it is not the first byte
-- It prints a byte as a sequence of two hex characters
- It prints a new line character
- It closes the file

XamBEE 17-Dec-15 9:19am

I get your point but i am not writing a file the method you mentioned.
here is my sample code......
void writefile(QString Filename)
{
QFile mFile(Filename);
if(!mFile.open(QFile::WriteOnly | QFile::Text))
{ qDebug() << "Not open file";
return;}
QTextStream mylog(&mFile);
mylog <<" "<< currtTimeStump ","<<"MsgDLC << ","<< frameID << ","<< Data << '\n';
mFile.close();

}
//Data contain QBYTEArray. which i want to make easily readable

Jochen Arndt 17-Dec-15 9:29am

Therefore I have written the last sentence in the solution because you did not mentioned in your question what method you are using.

I will update my solution.

XamBEE 17-Dec-15 9:52am

when QByteArray qba = 8000000000000000
output in .txt file is as following.
FFFFFF80 00 00 00 00 00 00 00 //first byte with three extra bytes.

Jochen Arndt 17-Dec-15 9:55am

Cast the byte array value:
(unsigned)qba.at(i)

XamBEE 17-Dec-15 10:08am

Still issue is there
when first byte is in range between 00-7F its correct but when its > 7F than output is FFFFFF80 ....

Jochen Arndt 17-Dec-15 10:38am

Don't know whom to blame more: Qt for using char as type for a byte array or the compiler (Microsoft?) for using signed chars.

Try casting with (unsigned char).