将 wchar_t 转换为 wstring

Question

I always convert wchar_t* to wstring with std::wstring x(y)

But it is not working in this code:

        wchar_t f = ctoupper(*cp);
        std::wstring cc(f); 

cp is a wchar_t*

Error in the std::wstring cc(f) line:

E0289   no instance of constructor "std::basic_string<_Elem, _Traits, _Alloc>::basic_string [with _Elem=wchar_t, _Traits=std::char_traits<wchar_t>, _Alloc=std::allocator<wchar_t>]" matches the argument list  

Whats wrong?

Answer 1

There is no wstring constructor for a single wchar_t value. You can achieve your intent with the following:

    std::wstring cc(1,f);   

You can also directly construct a wstring out of a c-style null-terminated wchar_t array:

    std::wstring cc(1,f);   // wstring made with a wchar_t f repeated 1 time
    std::wstring cg(cp);    // wstring made with a wchart_t null terminated array
    std::wcout<<cc<<std::endl<<cg<<std::endl; 

By the way, you can convert the full wstring to upper with:

    for (auto&x:cg) x=towupper(x);

( Online demo )

Alternatively you may prefer toupper(x,std::locale()) toa take into account conversion rules for non ascii characters in your current locale.