How to portably write std::wstring to file?

I have a wstring declared as such:

// random wstring
std::wstring str = L"abcàdëefŸg€hhhhhhhµa";

~~The literal would be UTF-8 encoded, because my source file is.~~

[EDIT: According to Mark Ransom this is not necessarily the case, the compiler will decide what encoding to use - let us instead assume that I read this string from a file encoded in e.g. UTF-8]

I would very much like to get this into a file reading (when text editor is set to the correct encoding)

abcàdëefŸg€hhhhhhhµa

but ofstream is not very cooperative (refuses to take wstring parameters), and wofstream supposedly needs to know locale and encoding settings. I just want to output this set of bytes. How does one normally do this?

EDIT: It must be cross platform, and should not rely on the encoding being UTF-8. I just happen to have a set of bytes stored in a wstring, and want to output them. It could very well be UTF-16, or plain ASCII.

Edit Report

1 Answer

There is a (Windows-specific) solution that should work for you here. Basically, convert wstring to UTF-8 codepage and then use ofstream.

#include < windows.h >

std::string to_utf8(const wchar_t* buffer, int len)
{
        int nChars = ::WideCharToMultiByte(
                CP_UTF8,
                0,
                buffer,
                len,
                NULL,
                0,
                NULL,
                NULL);
        if (nChars == 0) return "";

        string newbuffer;
        newbuffer.resize(nChars) ;
        ::WideCharToMultiByte(
                CP_UTF8,
                0,
                buffer,
                len,
                const_cast< char* >(newbuffer.c_str()),
                nChars,
                NULL,
                NULL); 

        return newbuffer;
}

std::string to_utf8(const std::wstring& str)
{
        return to_utf8(str.c_str(), (int)str.size());
}

int main()
{
        std::ofstream testFile;

        testFile.open("demo.xml", std::ios::out | std::ios::binary); 

        std::wstring text =
                L"< ?xml version=\"1.0\" encoding=\"UTF-8\"? >\n"
                L"< root description=\"this is a naïve example\" >\n< /root >";

        std::string outtext = to_utf8(text);

        testFile << outtext;

        testFile.close();

        return 0;
}

answered 2010-10-29T16:39:44.243

How to portably write std::wstring to file?

1 Answer

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