Output wstringstream by blocks issue

Question

I have some issue with reading wstringstream data. Code like this:

#include <iostream>
#include <sstream>

int main(int argc, char* argv[]) {
    std::wstringstream buf(L"dsadsadsad dsadsadsad sadsadsadsad sa dsadsadsads dasdsadsa");
    wchar_t sendbuf[5];
    wmemset(sendbuf, 0, 5);

    while (buf.read(sendbuf, 5))
    {
        std::wcout << sendbuf;
        wmemset(sendbuf, 0, 5);
    }
    return 0;
}

but it do not print out the whole data, Why?

Answer 1

The std::wostream::operator<< takes a wchar_t* parameter, so it can't know the length of your buffer. You need an extra space in your buffer for the terminating zero.

int main(int argc, char* argv[]) {
    std::wstringstream buf(L"dsadsadsad dsadsadsad sadsadsadsad sa dsadsadsads dasdsadsa");
    wchar_t sendbuf[6];
    wmemset(sendbuf, 0, 6);

    while (buf.read(sendbuf, 5))
    {
        std::wcout << sendbuf;
        wmemset(sendbuf, 0, 6);
    }
    return 0;
}

Answer 2

You are reading one wchar_t more than should be into buf, thus destroying the zero termination you did with wmemset(sendbuf, 0, 5); there.
If you change the read amount in the loop

    while (buf.read(sendbuf, 4))
                          // ^ change

it works as intended.

See live demo.