Is this possible to work with character arrays with Template Metaprogramming?

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I've written a series of templates to fill in a 32 character string based on up to 32 data types. Is it possible to compute this at compile time?

My assumption is no, but wanted to verify in case I was wrong.

Example of code to generate registration string with 3 data types

XML

temp[0]=Char_Type<T1>();
temp[1]=Char_Type<T2>();
temp[2]=Char_Type<T3>();
return temp;

Posted 7-Feb-11 20:49pm

T2102

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2 solutions

Solution 1

I'm not entirely sure what you're trying to achieve, but since each Char_Type<T> is a unique type, they can only be assigned to the same collection (in your case the temp[] array), if they're subclasses of the same base class (or an instance of that base class).

C++

class some_base
{
};
template<class T> class Char_Type : public some_base
{
public:
    T value;
    Char_Type()
    {
    };
    Char_Type(const T& v)
    {
        value = v;
    };
};
int main(int argc, char* argv[])
{
    some_base* a = new some_base[3];
    a[0] = Char_Type<char>('c');
    a[1] = Char_Type<int>(123);
    a[2] = Char_Type<int>(123.23);
    delete[] a;
    return 0;
}

But I think such a setup would cancel what you're trying to do.

Posted 7-Feb-11 23:07pm

Fredrik Bornander

Comments

T2102 8-Feb-11 7:47am

I am wondering if I can compute a one-to-one mapping from a series of types to characters using metaprogramming.

I currently have a template with a list of types such as T1, T2, ..., T15.
My code fills a character array with I-th position filled based on the I-th type.
I am wondering if I can compute the character array at compile time somehow.

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Niklas L · Accepted Answer · 2011-02-08T07:01:00

Maybe this would be some food for thought

C++

template<typename T> inline char char_type()       { return '-'; }
template<>           inline char char_type<char>() { return 'c'; }
template<>           inline char char_type<int>()  { return 'd'; }

template <typename T1, typename T2>
class MyClass
{
public:
    static char temp[]; // Will be init'ed at compile time
};

template <typename T1, typename T2>
char MyClass<T1, T2>::temp[] = { char_type<T1>(), char_type<T2>(), 0 };

int main()
{
    cout << MyClass<int, char>::temp << endl;
    cin.get();
    return 0;
}

Edit: Turned it into a working sample, and removed the constraints on the template parameters.