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Asked: 2026-05-11T15:56:26+00:00

When using a container class like vector , list , etc., I can use

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When using a container class like vector, list, etc., I can use the type of the elements by writing vector<type>::value_type.

However, the following code

template<class container> void foo(container& c) {     typedef container::value_type elementtype;     elementtype b; }

fails with the error ‘expected initializer before ‘elementtype’‘. Is it possible to infer the element type when the container type is given as a template argument or do I have to give the element type as an extra template argument?

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1 Answer

  1. You’re missing the required typename keyword:

    typedef typename container::value_type elementtype;

    This is because container is a dependent name in this template, so the compiler has no way of knowing whether container::value_type is always a type or not, as it may depend on the choice of container.

    Surely this question is a FAQ somewhere?

    Edit, it is: http://www.parashift.com/c++-faq-lite/templates.html#faq-35.18

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