Why isn’t the [] operator const for STL maps?

by

For std::map and std::unordered_map, operator[] will insert the index value into the container if it didn’t previously exist. It’s a little unintuitive, but that’s the way it is.

Since it must be allowed to fail and insert a default value, the operator can’t be used on a const instance of the container.

http://en.cppreference.com/w/cpp/container/map/operator_at

More Related Contents:

  1. Why isn’t it legal to convert “pointer to pointer to non-const” to a “pointer to pointer to const”
  2. What is meant with “const” at end of function declaration? [duplicate]
  3. Purpose of returning by const value? [duplicate]
  4. Do rvalue references to const have any use?
  5. How is a variable at the same address producing 2 different values? [duplicate]
  6. Const map element access
  7. int vs const int& [closed]
  8. What kind of optimization does const offer in C/C++?
  9. Deleting a pointer to const (T const*)
  10. Functions with const arguments and Overloading
  11. C++ Const Usage Explanation
  12. ‘const int’ vs. ‘int const’ as function parameters in C++ and C
  13. Why catch an exception as reference-to-const?
  14. What is the difference between const_iterator and non-const iterator in the C++ STL?
  15. Non-static const member, can’t use default assignment operator
  16. changing the value of const variable in C++ [duplicate]
  17. C/C++ changing the value of a const
  18. Why does C++ not have a const constructor?
  19. Calling a const function rather than its non-const version
  20. Why use a const member function?
  21. Easy rule to read complicated const declarations?
  22. What are top-level const qualifiers?
  23. Pointer to array with const qualifier in C & C++
  24. What is a constant reference? (not a reference to a constant)
  25. How to avoid code duplication implementing const and non-const iterators?
  26. Is it allowed to cast away const on a const-defined object as long as it is not actually modified?
  27. constexpr const vs constexpr variables?
  28. How to convert “pointer to pointer type” to const?
  29. C++: Why is const_cast evil?
  30. Is it safe to make a const reference member to a temporary variable?

Leave a Comment