typedef issue

This is a discussion on typedef issue within the C++ Programming forums, part of the General Programming Boards category; Code: template<typename Type> class GetTypeRegister { public: typedef Type::InnerClass type;//Errors on this line }; int main() { } I was ...

  1. #1
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    typedef issue

    Code:
    template<typename Type>
    class GetTypeRegister
    {
    public:
    	typedef Type::InnerClass type;//Errors on this line
    };
    int main()
    {
    }
    I was wondering why this doesn't compile. This is a simplified example of something that would be very useful to me in some template work I'm doing. I wouldn't think this template would be generated at all as I never use it, and so should not generate errors. Perhaps typedef's work in a different fashion than I expect.

    It generates the following errors and warnings (file paths cut for brevity).
    Code:
     
    warning C4346: 'Type::InnerClass' : dependent name is not a type
       prefix with 'typename' to indicate a type
       see reference to class template instantiation 'GetTypeRegister<Type>' being compiled
    error C2146: syntax error : missing ';' before identifier 'type'
    warning C4517: access-declarations are deprecated; member using-declarations provide a better alternative
    error C4430: missing type specifier - int assumed. Note: C++ does not support default-int

  2. #2
    Registered User valaris's Avatar
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    How does it know that InnerClass is a nested type and not some variable? Add typename like it says and perhaps it will work.

  3. #3
    and the hat of sweating
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    Code:
    typedef typename Type::InnerClass type;
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

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  4. #4
    C++まいる!Cをこわせ! Elysia's Avatar
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    Long story short, when working with anything that is a member of a template type, you must add typename before it (if it's a type).
    In your example, since Type is a template type to some class or something and InnerClass is a type, add typename.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  5. #5
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    Thank you, I'm still figuring out the subtleties of templates.

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