How to create const member function that accesses std::map item

Question

I am trying to merely return, not alter, the value in a `std::map`. It works, but if I put `const` on the function, as it should be, I get the error `No viable overloaded operator[] for type 'const std::map`. My code is as follows: ``` GLuint getCurrentColorAttribute() const { return m_programs[m_currentActiveProgram].attributes["SourceColor"]; } ``` Here is an image of the error in my IDE:

Accepted Answer

The `[]` operator of `std::map` isn't `const` (because it can create a new entry in the map if one doesn't exist), and thus you can't call it from a `const` function.

You can use `at` instead in `C++11`:

`return m_programs.at(m_currentActiveProgram).attribute["SourceColor"];`

How to create const member function that accesses std::map item

Solution

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