指向 char[] 类型成员的指针的模板签名

Question

I've written a comparator to check whether a member of an object is equal to an input. This works like a charm, except for a member which is a char[];

I've searched the internet, the C++ ISO standard and tried a lot, but I can't figure it out.

This is the simplified code:

/*
 * main.cpp
 *
 *  Created on: Nov 17, 2012
 *      Author: martijn
 */

#include <string.h>

class Data {
public:
    Data() {
        strcpy(Name, "MyCharArray");
    };
    virtual ~Data();

    char Name[12];
};

template <class ClassT, char (ClassT::*Name)[]> // What should be here?!
class Comparator {
public:
    Comparator() {};
    ~Comparator() {};
};

int main() {

    Comparator<Data, &Data::Name> comparatorArray;

    return 0;
}

The problem area (at least that's what I make of it) is indicated in the code. The present code is incorrect. The compiler says:

Error: could not convert template argument '&Data::Name' to 'char (Data::*)[]'

Answer 1

You need to specify the array bound in the template parameter type:

template <class ClassT, char (ClassT::*Name)[12]>

or possibly:

template <class ClassT, std::size_t N, char (ClassT::*Name)[N]>

and used:

// Note, this is a declaration of a function, is this correct?
Comparator<Data, 12, &Data::Name> comparatorArray();

Answer 2

An easy technique to answer this sort of question is using your compilers error messages.

Create a template function with a generic parameter that blatantly fails to compile when passed your parameter. Then look at the error message, it usually tells you what T is. My traditional fails to compile is an array of size zero: if your compiler is smart use int x[sizeof(T)-sizeof(expression with the same type as your test var)] but just a zero can work in some lazy compilers.