Convert function to qt notation

[Damian7546]

Hi,
Please help how convert this line: buffer.writeBigInt64LE(BigInt(number)) to qt ?
JS:

function int64LE(number) {
  const buffer = Buffer.alloc(8)
  buffer.writeBigInt64LE(BigInt(number))
  return buffer
}

qt:

QByteArray int64LE(quint64 number)
{
    QByteArray buffer[8];
    ......
    return buffer;

}

[jsulm]

@Damian7546 said in Convert function to qt notation:

qToLittleEndian(val, &le);

qToLittleEndian writes the result into the memory block the second parameter points to. And you're passing pointer to QByteArray!
It should be:

qToLittleEndian(val, le.data());

[Gaobo]

This post is deleted!

[Christian Ehrlicher]

Why manually when there are helper functions?
https://doc.qt.io/qt-6/qtendian.html

Oh, now deleted for unknown reasons.

[Gaobo]

Maybe you can ask chatgpt.....
This answer is from deepseek:

To convert the JavaScript function int64LE to Qt, you need to create a QByteArray that holds the little-endian byte representation of a 64-bit signed integer. Here's the step-by-step solution:

1. Resize the QByteArray to hold 8 bytes (64 bits).
2. Cast the input quint64 number to qint64 to handle it as a signed integer.
3. Extract each byte in little-endian order by masking and shifting the value.
4. Store each byte in the QByteArray.

QByteArray UtilsEssp::int64LE(quint64 number)
{
    QByteArray buffer;
    buffer.resize(8); // Allocate 8 bytes
    qint64 value = static_cast<qint64>(number); // Treat as signed

    // Extract each byte in little-endian order
    for (int i = 0; i < 8; ++i) {
        buffer[i] = static_cast<char>(value & 0xFF);
        value >>= 8;
    }

    return buffer;
}

Explanation:

• Resizing the Buffer: buffer.resize(8) ensures the QByteArray has space for 8 bytes.
• Casting to Signed: static_cast<qint64>(number) converts the unsigned input to a signed 64-bit integer, preserving the bit pattern.
• Little-Endian Extraction: The loop iterates 8 times, each time taking the least significant byte using value & 0xFF, then right-shifting value by 8 bits. This fills the QByteArray from the least significant byte to the most significant, achieving little-endian order.

This approach mirrors the original JavaScript functionality by directly manipulating the byte representation, ensuring compatibility with systems expecting a signed 64-bit integer in little-endian format.

[Damian7546]

@Christian-Ehrlicher said in Convert function to qt notation:

Why manually when there are helper functions?
https://doc.qt.io/qt-6/qtendian.html

Oh, now deleted for unknown reasons.

One way I use:

QByteArray m_data = QByteArray("\x0c\x06\x04\x04\x02\x00\x02\x00",8);
qint64 value =  qFromLittleEndian<qint64>(m_data);

but how change value to m_data using QtEndian and function qToLittleEndian ?

will the following be ok?

 QByteArray m_data;
  qToLittleEndian(value, &m_data );

[Christian Ehrlicher]

You should resize the QByteArray before

[Damian7546]

This post is deleted!

[Damian7546]

@Christian-Ehrlicher
Still doesn't work:

QByteArray qint64_2_LE(qint64 val)
{
    QByteArray le;
    le.resize(8);
    qToLittleEndian(val, &le);
    return le;
}

Application crashed after call qToLittleEndian function.

[jsulm]

@Damian7546 said in Convert function to qt notation:

qToLittleEndian(val, &le);

qToLittleEndian writes the result into the memory block the second parameter points to. And you're passing pointer to QByteArray!
It should be:

qToLittleEndian(val, le.data());