How to convert (const std::vector<unsigned char>& vchIn) to QByteArray?

Infinity

I have a function from a library which requires a const std::vector<unsigned char> as the second argument. The function declaration looks like this:

bool DecodeBase58(const std::string& str, std::vector<unsigned char>& vchRet);

My first parameter is a QByteArray and I would like to have the result also in a QByteArray. How can I convert const std::vector<unsigned char>& vchIn into a QByteArray? Or even better, how could I change the function below, that it returns a QByteArray?

static const char* pszBase58 = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";

bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch)
{
    // Skip leading spaces.
    while (*psz && isspace(*psz))
        psz++;
    // Skip and count leading '1's.
    int zeroes = 0;
    int length = 0;
    while (*psz == '1') {
        zeroes++;
        psz++;
    }
    // Allocate enough space in big-endian base256 representation.
    int size = strlen(psz) * 733 /1000 + 1; // log(58) / log(256), rounded up.
    std::vector<unsigned char> b256(size);
    // Process the characters.
    while (*psz && !isspace(*psz)) {
        // Decode base58 character
        const char* ch = strchr(pszBase58, *psz);
        if (ch == nullptr)
            return false;
        // Apply "b256 = b256 * 58 + ch".
        int carry = ch - pszBase58;
        int i = 0;
        for (std::vector<unsigned char>::reverse_iterator it = b256.rbegin(); (carry != 0 || i < length) && (it != b256.rend()); ++it, ++i) {
            carry += 58 * (*it);
            *it = carry % 256;
            carry /= 256;
        }
        assert(carry == 0);
        length = i;
        psz++;
    }
    // Skip trailing spaces.
    while (isspace(*psz))
        psz++;
    if (*psz != 0)
        return false;
    // Skip leading zeroes in b256.
    std::vector<unsigned char>::iterator it = b256.begin() + (size - length);
    while (it != b256.end() && *it == 0)
        it++;
    // Copy result into output vector.
    vch.reserve(zeroes + (b256.end() - it));
    vch.assign(zeroes, 0x00);
    while (it != b256.end())
        vch.push_back(*(it++));
    return true;
}

Christian Ehrlicher

See QByteArray(const char *data, int size)

fcarney

@Christian-Ehrlicher 's solution is the way to go. I got complicated on mine:

        std::vector<unsigned char> source = {'a'+0,'a'+1,'a'+2,'a'+3,'a'+4,'a'+5,'a'+6,'a'+7,'a'+8,'a'+9};
        QByteArray output; // empty byte array
        for(auto val: source){
            output.push_back(val);
        }

        // or use something from algorithm
        QByteArray output2;
        std::copy(source.begin(), source.end(), std::back_inserter(output2));

        qInfo() << output;
        qInfo() << output2;

Infinity

That is how I ended up doing it:

QByteArray encodeInput = "Hello world";
std::vector<unsigned char> encodeResultVector;
encodeResultVector.reserve(encodeInput.size());
for(int i = 0; i < encodeInput.size(); ++i)
    encodeResultVector.push_back(static_cast<unsigned char>(encodeInput.at(i)));
std::string encodeReslutStdString = EncodeBase58(encodeResultVector);
QByteArray encodedArray(encodeReslutStdString.c_str(), encodeReslutStdString.length());

qDebug() << "encode input  :" << encodeInput;
qDebug() << "encoded array :" << encodedArray;

QByteArray decodedArray;
std::vector<unsigned char> vchRet;
bool ret = DecodeBase58(encodedArray.constData(), vchRet);
decodedArray.reserve(vchRet.size());
for(size_t i = 0; i < vchRet.size(); ++i)
    decodedArray.append(vchRet.at(i));

qDebug() << "decoded array :" << decodedArray;

encode input  : "Hello world"
encoded array : "JxF12TrwXzT5jvT"
decoded array : "Hello world"

noone

std::vector<unsinged char> bson = ....
QByteArray qbson(reinterpret_cast<const char*>(bson.data()), bson.size());

QtCoder87

Can I ask why qt did not insert the static Function fromStdVectorUint8t to QByteArray?
you can make QString from 4 Basic_string variants char, char16_t, char32_t and wchar_t

why not bytearry from Std::vector<uint8_t> ?

JKSH

@QtCoder87 said in How to convert (const std::vector<unsigned char>& vchIn) to QByteArray?:

why not bytearry from Std::vector<uint8_t> ?

Mainly because there was little demand for it.

It is very easy to and cheap to reinterpret a uint8_t array as a char array, so QByteArray::fromStdUInt8Vector(const std::vector<uint_8> &vector) wouldn't add much value. Just use QByteArray(const char *data, int size).

Anyway, future code should not use uint8_t OR char. Instead, we should move towards std::byte.