如何在C ++中与派生类型匹配的元素上创建迭代器？ [英] How to create an iterator over elements that match a derived type in C++?

问题描述

我想在C ++中使用迭代器，它只能迭代特定类型的元素。在下面的示例中，我想仅迭代SubType实例的元素。

I'd like an iterator in C++ that can only iterate over elements of a specific type. In the following example, I want to iterate only on elements that are SubType instances.

vector<Type*> the_vector;
the_vector.push_back(new Type(1));
the_vector.push_back(new SubType(2)); //SubType derives from Type
the_vector.push_back(new Type(3));
the_vector.push_back(new SubType(4)); 

vector<Type*>::iterator the_iterator; //***This line needs to change***

the_iterator = the_vector.begin();
while( the_iterator != the_vector.end() ) {
    SubType* item = (SubType*)*the_iterator;
    //only SubType(2) and SubType(4) should be in this loop.
    ++the_iterator;
}

我如何用C ++创建这个迭代器？

How would I create this iterator in C++?

推荐答案

你必须使用动态演员。

the_iterator = the_vector.begin();
while( the_iterator != the_vector.end() ) {
    SubType* item = dynamic_cast<SubType*>(*the_iterator);
    if( item != 0 )
       ... 

    //only SubType(2) and SubType(4) should be in this loop.
    ++the_iterator;
}

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