C++ const iterator in Vector

Question

I am a newbie to C++. So, please bear with me. I was looking into the implementation of the std::vector class. I found the following 2 different implementation of the begin() method. I understand that the first one returns a RW iterator and the second one returns a read-only iterator. I thought that mere difference in return type is not enough for function overloading. How does this work then?

iterator
begin()
{ return iterator(this->_M_impl._M_start); }

const_iterator
begin() const
{ return const_iterator(this->_M_impl._M_start); }

One is `const`, the other isn't. That's enough for overloading. — Mat, Mar 16 '13 at 09:53
It's the standard library, [not STL](http://kera.name/articles/2010/08/it-is-not-called-the-stl-mmkay/). You can just refer to `std::vector`. — Angew is no longer proud of SO, Mar 16 '13 at 09:57

score 2 · Accepted Answer · edited May 23 '17 at 12:04

One is const and the other isn't. The const version will be called for const std::vector objects while the other is called for non-const std::vector objects. Also note that this also applies to const and non-const references and pointers.

More info on const methods and overloading:

Also relevant:

How many and which are the uses of "const" in C++?

score 0 · Answer 2 · answered Mar 16 '13 at 09:55

0

The implicit "this" parameter is const in the second method. This is enough to distinguish them in overloading.

answered Mar 16 '13 at 09:55

Emanuele Paolini

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C++ const iterator in Vector

2 Answers2