C++ templates

#include <cstring>
#include <type_traits>

// strcmp(handlers[i].inputFileExtension, inputFileExtension)
// handlers[i].inputFileExtension.cmp(inputFileExtension)

enum Constness
{
    Nonconst,
    NonConst = Nonconst,
    Cnst,
    Const = Cnst
};

template<Constness flag, typename T, typename U>
struct Select { typedef T Result; };

template<typename T, typename U>
struct Select<Nonconst, T, U> { typedef U Result; };

template <Constness isConst = Nonconst>
struct CString
{
    typedef typename Select<isConst, const char, char>::Result Char;
    Char * data;

    CString(Char * data)
    {
        this->data = data;
    }

    operator Char *()
    {
        return data;
    }


    Char& operator[](std::size_t idx)       { return this->data[idx]; }
    Char& operator[](std::size_t idx) const { return this->data[idx]; }

    CString * operator=(CString * other)
    {
        this->data = other.data;
        return *this;
    }

    inline int cmp(const char * rhs) const {
        return std::strcmp(this->data, rhs);
    }
};

struct CommandHandler
{
    CString<Const> inputFileExtension;
    CString<> outputFileExtension;
};

struct CommandHandler2
{
    const char * inputFileExtension;
    char * outputFileExtension;
};

char png_str1[] = "png";
char png_str2[] = "png";

struct CommandHandler handlers[] =
{
    { "1bpp", png_str1},
    { "4bpp", png_str2}
};

struct CommandHandler2 handlers2[] =
{
    { "1bpp", png_str1},
    { "4bpp", png_str2}
};

int main2(const char * inputFileExtension)
{
    if (handlers[0].inputFileExtension.cmp(inputFileExtension) == 0) {
        char t3bpp_str[] = "3bpp";
        handlers[0].outputFileExtension = t3bpp_str;
        handlers[0].inputFileExtension = "9bpp";
        return 10;
    } else {
        return 17;
    }
}

int main3(const char * inputFileExtension)
{
    if (strcmp(handlers2[0].inputFileExtension, inputFileExtension) == 0) {
        char t3bpp_str[] = "3bpp";
        handlers2[0].outputFileExtension = t3bpp_str;
        handlers2[0].inputFileExtension = "9bpp";
        return 10;
    } else {
        return 17;
    }
}