C++ pass inner structure as parameter

Question

There is a structure TOut containing inner structure TIn:

template <typename T>
struct TOut
{
    struct TIn
    {
            bool b;
    };

    TIn in;
T t;
};

How to correctly pass TIn in as a formal parameter of some method?

class Test
{
public:
    template <typename T>
    static void test ( const TOut<T>::TIn &i) {} //Error
};


int main()
{
TOut <double> o;
Test::test(o.in);
}

The program compiles with the following error:

Error   4   error C2998: 'int test' : cannot be a template definition

http://stackoverflow.com/questions/7178948/problem-with-functions-accepting-inner-classes-of-template-classes — Lol4t0, Jan 25 '12 at 20:24
@TJD `Tin` would be a known ("concrete") type if it where declared beside `Tout`, or inside a non-template class. At the point where the OP is getting an error, `Tin` is not yet known, because `TOut` is not yet instantiated. BTW, the term "concrete" is normally used in the context of inheritance (opposite of "abstract"). — Emile Cormier, Jan 25 '12 at 20:38

score 7 · Accepted Answer · edited May 23 '17 at 10:32

7

You need to use the typename keyword:

template <typename T>
static void test ( const typename TOut<T>::TIn &i) {}

See Where and why do I have to put the "template" and "typename" keywords?

edited May 23 '17 at 10:32

Community

1
1

answered Jan 25 '12 at 20:24

Emile Cormier

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score 2 · Answer 2 · answered Jan 25 '12 at 20:39

2

Why cannot you use the simpler

template <typename T>
static void test (const T& i)

instead?

answered Jan 25 '12 at 20:39

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C++ pass inner structure as parameter

2 Answers2