Is there a shorter way to initialize a QByteArray?

问题

In my program I work a lot with serial communication so QByteArray is used very often.

I was wondering if there was a shorter way to initialize a QByteArray with specific bytes than:

const char test_data[] = {
    static_cast<char>(0xB1), static_cast<char>(0xB2),
    0x5, static_cast<char>(0xFF),
    static_cast<char>(0xEE), static_cast<char>(0xEE),
    static_cast<char>(0x0)}; // Note QByteArray should be able to hold 0 byte
const QCanBusFrame frame = QCanBusFrame(0xA1, QByteArray(test_data));

The static_cast<char> is necessary because otherwise C++11 gives an error about narrowing, because the range 0x7F to 0xFF is bigger than a char could fit--but a char is what the QByteArray constructor asks for.

This is the QByteArray constructor being used:

QByteArray::QByteArray(const char *data, int size = -1)

回答1:

Simple and effective:

QByteArray b = QByteArrayLiteral("\x12\x00\xa4\x42\x51\x00\x00\x99");

回答2:

As an alternative to QByteArrayLiteral, you can roll your own, if you wish:

#include <QByteArray>

template <int N> QByteArray arrayFromLiteral(const char (&data)[N]) {
   return QByteArray::fromRawData(data, N-1);
}

int main() {
   const auto arr = arrayFromLiteral("\xB1\xB2\0\1");
   Q_ASSERT(arr.size() == 4);
   Q_ASSERT(arr[0] == (char)0xB1);
   Q_ASSERT(arr[1] == (char)0xB2);
   Q_ASSERT(arr[2] == (char)0x00);
   Q_ASSERT(arr[3] == (char)0x01);
}

回答3:

like this:

const unsigned char str[] = {0xff, 0xed, 0xba, 0xd1};
QByteArray ba(reinterpret_cast<const char*>(&str[0]),std::extent<decltype(str)>::value);

now QByteArray constructor looks weird, but byte sequences are clear. You can also add terminating 0-byte to array instead of using std::extent, but in general you can have zero-bytes in the middle of sequence.

回答4:

Being inspired by the answers above this is what I finally came up with:

const quint8 testData[] {0xB1, 0x00, 0xB2, 0x00};
const QCanBusFrame cFrame = QCanBusFrame(
    0xA1, QByteArray(reinterpret_cast<const char*>(testData), sizeof(testData)));

I much prefer to have the bytes as byte numbers rather than literal characters when working with serial communication.

After having a discussion on ##c++ I was advised that reinterpret_cast is appropriately used in this situation.

回答5:

May be works slowly:

QByteArray ba = QByteArray::fromHex(QVariant("B1B2FFEEEE00").toByteArray());

回答6:

Have you tried the following:

const unsigned char test_data[] = {
    static_cast<char>(0xB1), static_cast<char>(0xB2),
    0x5, static_cast<char>(0xFF),
    static_cast<char>(0xEE), static_cast<char>(0xEE),
    static_cast<char>(0xB3)};
const QCanBusFrame frame = QCanBusFrame(0xA1, QByteArray((char*)test_data));

You are using the constructor: QByteArray::QByteArray(const char *data, int size = -1).

If size is negative, data is assumed to point to a nul-terminated string and its length is determined dynamically. The terminating nul-character is not considered part of the byte array.

来源：https://stackoverflow.com/questions/36327327/is-there-a-shorter-way-to-initialize-a-qbytearray

标签

c++

c++11

qbytearray

qt5.6