String in WinAPI and C ++ I / O

Question

I teach my own WinAPI in C ++, but as I progress, I notice that every function in WinAPI returns either char *, DWORD, LPCSTR, etc. I am worried about using a string, so what I do after getting the return value is I convert it to a string. Is it good or bad? or does it matter if I convert it every time? or it will make the process slow or any bad things. And for I / O in C ++, which is better than cout or printf, given the exe size or performance / functionality issues?

Answer 1

Start by exploring the different types of strings. For example, char*, LPSTRand LPCSTRare connected with each other and retain ANSI symbols; the latter is a pointer to a constant string. Similarly wchar_t*, WCHAR*, LPWSTRand LPCWSTRare connected and stored Unicode characters; again, the last is a pointer to a constant string.

Then look what you mean when you say something like “returns char *”, since most Windows APIs do nothing. Instead, they take LPSTR(a pointer to a char buffer) or LPWSTR(a pointer to a WCHAR buffer) and write to the buffer. These APIs again almost always take the number of characters available in the buffer, or have document buffer size requirements such as MAX_PATH.

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std::wstring GetEnvironmentVariable(const std::wstring& strName)
{
    DWORD cchValue = MAX_PATH;
    std::wstring strValue;

    // call API once or twice, to get required buffer size
    strValue.resize(cchValue);
    cchValue = GetEnvironmentVariable(strName.c_str(), &strValue[0], cchValue);
    if (cchValue > MAX_PATH)
    {
        strValue.resize(cchValue);
        cchValue = GetEnvironmentVariable(strName.c_str(), &strValue[0], cchValue);
    }

    // process errors such as ERROR_ENVVAR_NOT_FOUND
    if (0 == cchValue)
    {
        // throw exception? return empty string? (current code does latter)
    }

    // remove null character and any extra buffer
    strValue.resize(cchValue);
    return strValue;
}

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Answer 2

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