How to convert char* to wchar_t*?

In your example, wc is a local variable which will be deallocated when the function call ends. This puts you into undefined behavior territory.

The simple fix is this:

const wchar_t *GetWC(const char *c)
{
    const size_t cSize = strlen(c)+1;
    wchar_t* wc = new wchar_t[cSize];
    mbstowcs (wc, c, cSize);

    return wc;
}

Note that the calling code will then have to deallocate this memory, otherwise you will have a memory leak.