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Editorial Team
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Asked: 2026-05-23T15:13:55+00:00

class MyString { public: MyString(const std::wstring& s2) { s = s2; } operator LPCWSTR()

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class MyString
{
public:
    MyString(const std::wstring& s2)
    {
        s = s2;
    }

    operator LPCWSTR() const
    {
        return s.c_str();
    }
private:
    std::wstring s;
};

int _tmain(int argc, _TCHAR* argv[])
{
    MyString s = L"MyString";
    CStringW cstring = L"CString";
    wprintf(L"%s\n", (LPCWSTR)cstring); // Okay. Becase it has an operator LPCWSTR()
    wprintf(L"%s\n", cstring); // Okay, fine. But how?        
    wprintf(L"%s\n", (LPCWSTR)s); // Okay. fine.
    wprintf(L"%s\n", s); // Doesn't work. Why? It prints gabage string like "?."
    return 0;
}

How can CString be passed to format string %s?

By the way, MSDN says(it’s weird)

To use a CString object in a variable argument function
Explicitly cast the CString to an LPCTSTR string, as shown here:

CString kindOfFruit = "bananas";
int      howmany = 25;
printf( "You have %d %s\n", howmany, (LPCTSTR)kindOfFruit );
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1 Answer

  1. Editorial Team

    CString is specifically designed such that it only contains a pointer that points to the string data in a buffer class. When passed by value to printf it will be treated as a pointer when seeing the “%s” in the format string.

    It originally just happened to work with printf by chance, but this has later been kept as part of the class interface.

    This post is based on MS documentation long since retired, so I cannot link to their promise that they will continue to make this work.

    However, before adding more downvotes please also read this blog post from someone sharing my old knowledge:

    Big Brother helps you

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