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typedef within template class

Rothbard
Rothbard asked
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Last Modified: 2013-12-31
I have a vector class with the following typedefs

template <class T> class Vec
{
public:
	// definitions
	typedef T* iterator;
	typedef const T* const_iterator;
	typedef T value_type;
	typedef size_t size_type;
	typedef std::ptrdiff_t difference_type;
	typedef T& reference;
	typedef const T& const_reference;
[...]}

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Everything works fine, but when I want to implement an erase method to mimic the STL one, I find that I can only use iterator instead of T* (as per the typedef above) if I include the function definition within the Vec class definition. If on the other hand I only declare erase within the class definition as follows:

iterator erase(iterator it);

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Then I can't define it externally in Vec.cpp as

template <class T> iterator Vec<T>::erase(iterator it) {[...]}

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but I need to use T* instead of iterator:

template <class T> T* Vec<T>::erase(T* it) {[...]}

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which sort of defeats the purpose of using the typedef.

Why does this happen? Is there any way around it?
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jkr
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Top Expert 2012

Commented:
In your case, 'iterator' has global scope, not the scope of 'Vec<T>' - did you mean

template<class T> Vec<T>::iterator Vec<T>::erase(Vec<T>::iterator it) { /* ... */ }

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?

Author

Commented:
Sorry, that's what I meant. However, if I do that I get the following warning message:

Warning      1      warning C4346: 'Vec<T>::iterator' : dependent name is not a type      

which is followed by several errors, some of which I have copied below.

Error      2      error C2143: syntax error : missing ';' before 'Vec<T>::erase'
Error      3      error C2065: 'T' : undeclared identifier
Error      4      error C2923: 'Vec' : 'T' is not a valid template type argument for parameter 'T'
Error      5      error C2146: syntax error : missing ')' before identifier 'it'
Error      6      error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
Error      7      error C2350: 'Vec<T>::erase' is not a static member      
Error      8      error C2059: syntax error : ')'
Senior Software Engineer (Avast)
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Commented:
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evilrixSenior Software Engineer (Avast)
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Commented:
Oh, and you will probably find that implementing iterators is a lot simpler if you use the standard iterator and iterator traits framework.

http://www.cplusplus.com/reference/iterator/iterator_traits/
http://www.cplusplus.com/reference/iterator/iterator/

Author

Commented:
Thanks for the replies.
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