Thread: syntax for a tricky class template static member definition

  1. #1
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    syntax for a tricky class template static member definition

    I have a class template with an iterator as a static member. Below is a simplified version of the code. I'm having trouble with the proper syntax for the definition (line 9). Can anyone help?
    Code:
    #include <vector>
    
    template<typename T>
    class A {
      static typename std::vector<typename std::vector<A*>::iterator>::iterator p;
    };
    
    template<typename T>
    typename A<T>::std::vector<std::vector<A<T>*>::iterator>::iterator p;
    
    int main() {}
    Compiling with g++ gives

    foo.cpp:9: error: non-template ‘vector’ used as template
    foo.cpp:9: note: use ‘typename A<T>::std::template vector’ to indicate that it is a template
    foo.cpp:9: error: expected unqualified-id before ‘;’ token

  2. #2
    Guest Sebastiani's Avatar
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    it should be:

    Code:
    template<typename T>
    typename std::vector<typename std::vector<A<T>*>::iterator>::iterator A<T>::p;
    Code:
    #include <cmath>
    #include <complex>
    bool euler_flip(bool value)
    {
        return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) 
            * std::complex<float>(std::atan(1.0)
            *(1 << (value + 2)))
        ).real() < 0;
    }

  3. #3
    and the hat of sweating
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    Code:
    #include <vector>
    
    template<typename T>
    class A {
      static typename std::vector<typename std::vector<A<T>*>::iterator>::iterator p;
    };
    
    template<typename T>
    typename std::vector<typename std::vector<A<T>*>::iterator>::iterator A<T>::p;
    
    int main()
    {
       return 0;
    }

  4. #4
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    cpjust: Yes, that works! Thanks. Sebastiani: Yes, I should have seen that, though that change by itself didn't fix it. However, also changing A* to A<T>* in the class declaration as in cpjust's code solved it.

  5. #5
    Guest Sebastiani's Avatar
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    your right. time to turn up the warnings, I suppose.
    Code:
    #include <cmath>
    #include <complex>
    bool euler_flip(bool value)
    {
        return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) 
            * std::complex<float>(std::atan(1.0)
            *(1 << (value + 2)))
        ).real() < 0;
    }

  6. #6
    C++まいる!Cをこわせ!
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    I encountered that problem recently...
    You can't pass a non-specialized class as a template type. Since class A is a template class, just typing A is illegal, instead you to give it a type, so A<T> would fix that.
    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.

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