Qt：QVector <bool> 到QByteArray

Question

Hello please help me with convertion. QVector of bool to array of bytes.

QByteArray currentArray
//get(currentArray); currentArray is just text.
QMap <QChar, QVector<bool> > table;
//creating table;
//table: is set of QChar and bit code
//0: 100110111001
//1: 00011
//2: 011110
//3: 010001
//...
QByteArray compressedArray;
//converting QVector<bool> from QMap to QByteArray
//it do not work fine.
int count=0;
Сhar buf=0;
i=0;

while(i<currentArray.size())
{
    QVector <bool> x = table[currentArray.at(i++)];
    for(int n=0; n < x.size(); n++)
    {
        buf = buf | x[n] << (7 - count);
        count ++;
        if (count == 8)
        {
            count=0;
            compressedArray += buf;
            buf = 0;
        }
    }

}

This is an implementation of the algorithm Huffman. Decryption works correctly, so problem is here.

Answer 1

I can't say what the exact cause of your problem is but there are several issues in your code that could cause problems:

QVector <bool> x = table[currentArray.at(i++)];

1. a char returned by currentArray.at() is implicitly converted to a QChar - for values > 127 this might be a problem and lookup the wrong value, this depends how the lookup was created. => better use QMap or even QVector with 256 entries having char as index which is much faster.

2. table[...] will insert a new empty entry to the map if no one exists for the key. I don't think this is intended here - better use table.value().

Also I don't remember but I think huffman stores bits starting at bit 0 and then filling up to most significant bits, so maybe

 buf = buf | x[n] << (7 - count);

should be the other way round?

Good luck.