Convert string to wstring using wsprintf

Question

I was trying to create a function that converts a string to a wstring, using the built-in function wsprintf.

For some reason, when I try to print the result wstring, nothing is printed, and when I try debugging, I saw it contains letters in Chinese (so I guess that the problem is that the sprintf function didn't add a leading zero-byte to each character for some reason, but I have no idea WHY).

Can someone please help me figure it out?

Here is what I did:

#include <iostream>
#include <string>

using std::wstring;
using std::string;
using std::wcout;
using std::endl;

wstring strToWstr(const string& str);

int main()
{
    string str = "test";
    wstring wstr = strToWstr(str);
    wcout << wstr << endl;
}

wstring strToWstr(const string& str)
{
    wchar_t* temp = NULL;

    temp = new wchar_t[str.length() + 1]; //allocated string with the right length

    swprintf(temp, str.length() + 1, L"%s", str.c_str());

    wstring res = temp;

    delete[] temp;
    return res;
}