Constructing with a reference to an const array of const structs

Question

So I have an array of structures and a class that uses the array. The constructor needs to reference the array of structures which are a constant. What I am struggling with is passing the array of structures as a reference so that the class constructor can use it. Since the array of structures doesn't change there is no need to copy it, I just need to reference it. Here is my current code which generates errors.

struct c_cs_pair_t
{
    const wchar_t c;
    const wchar_t* cs;
};


class Converter
{
protected:
    size_t  _length;
    const c_cs_pair_t(& _pairs)[];

public:

    Converter ( const c_cs_pair_t(& pairs)[] ) : _pairs(pairs) {
        _length = sizeof ( pairs ) / sizeof( c_cs_pair_t );
    }

};

const c_cs_pair_t c2cspairs[] = 
        { { L'\n', L"\\n" }
        , { L'\0', L"\\0" }
        , { L'\\', L"\\\\" }
        , { L'[', L"\\[" }
        , { L']', L"\\]" }
        , { L'.', L"\\." }
        , { L':', L"\\:" }
        , { L'\u0008', L"\\b" }
        , { L'\u000c', L"\\f" }
        , { L'\u000a', L"\\n" }
        , { L'\u000d', L"\\r" }
        , { L'\u0009', L"\\t" }
        , { L'\u000b', L"\\v" }
        , { L'\u0000', L"\\0" }
        };

const Converter converter ( c2cspairs );

When I compile I get compilation errors complaining there is no matching candidate.

How do I pass the array to the constructor so the class methods can use it. The array knows it's size implicitly as it is a constant.

*Possible* duplicate: [C++ pass array by reference](https://stackoverflow.com/q/10007986/10871073)? — Adrian Mole, Jul 09 '20 at 23:22

cigien · Accepted Answer · 2020-07-09T23:48:32.017

You need to specify the size of the array using a template parameter:

template<size_t N>
class Converter
{
protected:
    size_t  _length;
    const c_cs_pair_t(& _pairs)[N];

public:
    Converter ( const c_cs_pair_t(& pairs)[N] ) : _pairs(pairs) {
        _length = N;
    }
};

Note that you don't really need the _length member any longer.

Here's a demo. Note that this only works from c++17 with the introduction of class template argument deduction.

Constructing with a reference to an const array of const structs

1 Answers1