About qbytearray storage hexadecimal and hexadecimal conversion

Summary

1、Qt in QByteArray Store hexadecimal numbers （ for example 0xff）, In fact, it is based on ASCII Code stored , The storage form is '\xff'（ among \ It's a transcoding identifier ）, Unit is byte （ A byte stores a hexadecimal number ） If you need to compare , use array.at(0) == '\xff' Express , instead of array.at(0) == 0xff .

2、 Judge QByteArray What's in it is int Integers , Or characters 'f'： If it is int Integers , Then use int perhaps hex To judge , If it's a character ‘f’ , Then use ‘f’ To judge .

• such as QByteArray The content is ff , namely QByteArray[0] = f,QByteArray[1] = f, be QByteArray There are two characters stored ‘f’, Not integers 255.
• such as QByteArray The content is ff , namely QByteArray[0] = ff, be QByteArray It stores an integer 255, Not two characters ‘ff’.

notes ： stay QByteArray in \xff And 0xff It's equivalent .

Hexadecimal conversion （ Commonly used in serial port and network communication ）

int dec = 14 ;

int dec = 20;
// Decimal to hexadecimal ( Retain 4 position )
qDebug() << QString(“%1”).arg(dec, 4, 16, QLatin1Char(‘0’)); //Return “0014”
// Decimal to binary （ At least keep 4 position ）
qDebug() << QString(“%1”).arg(dec, 4, 2, QLatin1Char(‘0’)); //Return “10100”

// Hexadecimal to decimal
QString hex = “14”;
qDebug() << hex.toInt(&ok, 16); //return 20
// Binary to decimal
QString byte = “10100”;
qDebug() << byte.toInt(&ok, 2); //return 20

Text to hexadecimal conversion （ Commonly used in serial port and network communication ）

QString strT1 = “Qt is great!”;
qDebug() << strT1.toLatin1(); // return: “Qt is great!”
qDebug() << strT1.toLatin1().data(); // return: Qt is great!
qDebug() << strT1.toLatin1().toHex(); // return: “517420697320677265617421”

QString strT2 = “517420697320677265617421”;
qDebug() << QByteArray::fromHex(strT2.toLatin1()); // return: “Qt is great!”
qDebug() << QByteArray::fromHex(strT2.toLatin1().data()); // return: “Qt is great!”
qDebug() << QByteArray::fromHex(strT2.toLatin1().toHex()); //
// Construct a QByteArray ba, The incoming parameter is const char*
QByteArray ba(“010203”);

//ba Save one character by one
qDebug()<<“1:”<<ba; //“010203”

// Convert characters into 10 The base number corresponds to 16 Hexadecimal Numbers
qDebug()<<“2:”<<ba.toHex(); //“303130323033”

// Convert one character into two characters into a number 16 Hexadecimal said
qDebug()<<“3:”<<QByteArray::fromHex(ba); //“\x01\x02\x03”

Press 16 Binary printing QByteArray ba

printf( " data: " );

for (int i = 0; i < ba.length(); i++)
printf(“%02x ”, ba[i]);
printf(“\n”);