Function to print data type to debug console-CodePudding

While searching for any kind of function in could help printing data to debug console, I've found this function here on StackOverflow that can print almost any kind of data:

template <typename Arg, typename... Args>
void doPrint(Arg&& arg, Args&&... args)
{
    std::stringstream out;

    out << std::forward<Arg>(arg);
    using expander = int[];
    (void)expander {
        0, (void(out << std::left << std::setw(20) << std::forward<Args>(args)), 0)...
    };

    OutputDebugStringA(out.str().c_str());
}

But it doesn't work when I try to pass a wstring to it, ex:

std::wstring color = L"blue";
doPrint("color: ", color);

I get this error:

Error    C2679    binary '<<': no operator found which takes a right-hand operand of type 'std::wstring' (or there is no acceptable conversion)

Is it possible to also support wstring?

I tried to change std::stringstream to std::wstringstream, but now I get error on OutputDebugStringA():

void OutputDebugStringA(LPCSTR)': cannot convert argument 1 from 'std::basic_string<wchar_t,std::char_traits<wchar_t>,std::allocator<wchar_t>>' to 'LPCSTR'

CodePudding user response：

By default, you can't print a std::wstring to a char-based std::ostream, such as std::stringstream, because std::basic_ostream<char> (aka std::ostream) does not have an overloaded operator<< defined for std::wstring (or const wchar_t*).

You could define your own operator<< for that purpose, which converts a std::wstring to a std::string/char* using WideCharToMultiByte() or equivalent conversion, and then print that instead, eg:

std::ostream& operator<<(std::ostream &os, const std::wstring &wstr)
{
    int len = WideCharToMultiByte(CP_ACP, 0, wstr.c_str(), wstr.size(), nullptr, 0, nullptr, nullptr);
    if (len > 0) {
        std::string str;
        str.resize(len);
        WideCharToMultiByte(CP_ACP, 0, wstr.c_str(), wstr.size(), str.data()/* or: &str[0] */, len, nullptr, nullptr);
        os << str;
    }
    return os;
}

template <typename Arg, typename... Args>
void doPrint(Arg&& arg, Args&&... args)
{
    std::stringstream out;

    out << std::forward<Arg>(arg);
    using expander = int[];
    (void)expander {
        0, (void(out << std::left << std::setw(20) << std::forward<Args>(args)), 0)...
    };

    OutputDebugStringA(out.str().c_str());
}

Online Demo

Otherwise, you need a wchar_t-based std::basic_ostream<wchar_t> (aka std::wostream) instead, such as std::wstringstream, using OutputDebugStringW() for the logging (unless you convert the output std::wstring to std::string to log with OutputDebugStringA()). Fortunately, std::basic_ostream<CharT> does have an overloaded operator<< for const char* strings (but not std::string) regardless of whether CharT is char or wchar_t, so std::wstringstream can print the pointer returned by std::string::c_str(), eg:

std::wostream& operator<<(std::wostream &os, const std::string &str)
{
    os << str.c_str();
    return os;
}

template <typename Arg, typename... Args>
void doPrint(Arg&& arg, Args&&... args)
{
    std::wostringstream out;

    out << std::forward<Arg>(arg);

    using expander = int[];
    (void)expander {
        0, (void(out << std::left << std::setw(20) << std::forward<Args>(args)), 0)...
    };

    OutputDebugStringW(out.str().c_str());
}

Online Demo