operator[] and std::map

[Gawain Bolton]

Gilbert Laycock wrote:

> Should it be possible to use operator[] from std::map in a const
> context?
>
> For example, in class A, the isFive method will not compile (g++
> 3.2.3) because _m[c] does not preserve const. In contrast std::vector
> provides a const version of operator[].

No, there cannot be a const version of operator[] for std::map since, if
the key passed is not already present in the map, it will be added with
an associated value constructed using value_type's default constructor.

What you must do is use "find()" and, if the key is present in the map,
check the associated value.


Gawain

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