Qbytearray easy question

[arturs]

Could you write me proper code for my code

QByteArray test ;
   test[0] = 0xFF;
  unsigned char ch = 0;
 
   ch = 0xff;
   if (test.at(0)==ch) qDebug () << "OK";
 
   qDebug () << ch;
 
   qDebug () << test.at(0);

QByteArray test ;
   test[0] = 0xFF;
  unsigned char ch = 0;

   ch = 0xff;
   if (test.at(0)==ch) qDebug () << "OK";

   qDebug () << ch;

   qDebug () << test.at(0);

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because test[0] is signed and ch is unsigned the condition is false. I will try to use your method but without success.

[Radek]

Try

if( (unsigned char)(test.at(0)) == ch ) qDebug() << "OK";

if( (unsigned char)(test.at(0)) == ch ) qDebug() << "OK";

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[arturs]

It works perfectly :

Thank you for help

[arturs]

I have additional qestion

QByteArray test;
        test[0]= 0xAB;
        test[1]= 0xCD;
        test[2]= 0xEF;
        test[3]= 0x01;
        test[4]= 0x02;
        test[5]= 0x03;
        test[6]= 0x04;

QByteArray test;
        test[0]= 0xAB;
        test[1]= 0xCD;
        test[2]= 0xEF;
        test[3]= 0x01;
        test[4]= 0x02;
        test[5]= 0x03;
        test[6]= 0x04;

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I need to take only the following bytes
test[1]= 0xCD;
test[2]= 0xEF;
test[4]= 0x02;
test[5]= 0x03;

and show it as a single number

0xCDEF0203 = 3454992899

I try to use the code but it does not work

usnigned long num;
num |= (unsigned char)(test[1]) << 8;
num |= (unsigned char)(test[2]) << 8;
num |= (unsigned char)(test[4]) << 8;
num |= (unsigned char)(test[5]) << 8  ;

usnigned long num;
num |= (unsigned char)(test[1]) << 8;
num |= (unsigned char)(test[2]) << 8;
num |= (unsigned char)(test[4]) << 8;
num |= (unsigned char)(test[5]) << 8  ;

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Why it does not work ? Maybe is it easier method to do it ?

Regards
Artur

[ars]

First, in your code the variable num is not initialized before you apply operator |= to it. Second, you shift each of the test[] values by 8 bit and combine the shifted value into num. What you need to do is: initialize num to test[1]. Before adding test[2], shift num by 8 bit and then add test[2]. Same procedure for test[4] and test[5]. It may look like

unsigned long num       = (unsigned char)(test[1]) ;
num = num << 8; num |= (unsigned char)(test[2]) ;
num = num << 8; num |= (unsigned char)(test[4]) ;
num = num << 8; num |= (unsigned char)(test[5]) ;

unsigned long num       = (unsigned char)(test[1]) ;
num = num << 8; num |= (unsigned char)(test[2]) ;
num = num << 8; num |= (unsigned char)(test[4]) ;
num = num << 8; num |= (unsigned char)(test[5]) ;

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[arturs]

Yes. It works.

I have last question.

How to convert my QbyteArray test to QString ?

Regards
Artur

[ars]

See the constructors for QString (http://doc.qt.io/qt-4.8/qstring.html). You can do

QString s(test);

QString s(test);

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to initalize QString s from QByteArray test. From the documentation:

QString::QString(const QByteArray & ba)

Constructs a string initialized with the byte array ba. The given byte array is converted to Unicode using fromAscii(). Stops copying at the first 0 character, otherwise copies the entire byte array.

You can disable this constructor by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

[Radek]

Please check the Qt classes reference before posting on the forum.

The wanted QString is produced by "fromXXX" static members of QString. If the QByteArray contains UTF8 data (as a byte array) then

QString test2str = QString::fromUtf8(test);

QString test2str = QString::fromUtf8(test);

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There are more "fromXXX" functions defined in QString.