How to convert QByteArray to a byte string?

Question

I have a QByteArray object with 256 bytes inside of it. However, when I try to convert it to a byte string ( std::string ), it comes up with a length of 0 to 256. It is very inconsistent with how long the string is, but there are always 256 bytes in the array. This data is encrypted and as such I expect a 256-character garbage output, but instead I am getting a random number of bytes.

Here is the code I used to try to convert it:

// Fills array with 256 bytes (I have tried read(256) and got the same random output)
QByteArray byteRecv = socket->read(2048);
// Gives out random garbage (not the 256-character garbage that I need)
string recv = byteRecv.constData();

The socket object is a QTcpSocket* if it's necessary to know.

Is there any way I can get an exact representation of what's in the array? I have tried converting it to a QString and using the QByteArray::toStdString() method, but neither of those worked to solve the problem.

Answer 1

QByteArray::constData() member function returns a raw pointer const char* . The constructor of std::string from a raw pointer

std::string(const char* s);

constructs the string with the contents initialized with a copy of the null-terminated character string pointed to by s . The length of the string is determined by the first null character. If s does not point to such a string, the behaviour is undefined.

Your buffer is not a null-terminated string and can contain null characters in the middle. So you should use another constructor

std::string(const char* s, std::size_type count);

that constructs the string with the first count characters of character string pointed to by s .

That is:

std::string recv(byteRecv.constData(), 256);

---

For a collection of raw bytes, std::vector might be a better choice. You can construct it from two pointers:

std::vector<char> recv(byteRecv.constData(), byteRecv.constData() + 256);