Const correctness in C vs C++

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In addition to the differences you cite, and the library differences that
Steve Jessop mentions,

char* p1;
char const* const* p2 = &p1;

is legal in C++, but not in C. Historically, this is because C
originally allowed:

char* p1;
char const** p2 = &p1;

Shortly before the standard was adopted, someone realized that this
punched a hole in const safety (since *p2 can now be assigned a
char const*, which results in p1 being assigned a char const*); with
no real time to analyse the problem in depth, the C committee banned any
additional const other than top level const. (I.e. &p1 can be
assigned to a char ** or a char **const, but not to a char const**
nor a char const* const*.) The C++ committee did the further
analysis, realized that the problem was only present when a const
level was followed by a non-const level, and worked out the necessary
wording. (See ยง4.4/4 in the standard.)

More Related Contents:

  1. Differences with const keyword in C++
  2. Meaning of ‘const’ last in a function declaration of a class?
  3. How to convert a std::string to const char* or char*
  4. Is it better in C++ to pass by value or pass by constant reference?
  5. How do I remove code duplication between similar const and non-const member functions?
  6. Use of ‘const’ for function parameters
  7. Const before or const after?
  8. Why can’t I initialize non-const static member or static array in class?
  9. Does const mean thread-safe in C++11?
  10. Is it better in C++ to pass by value or pass by reference-to-const?
  11. C++ Const Usage Explanation
  12. Does const-correctness give the compiler more room for optimization?
  13. C++ – enum vs. const vs. #define
  14. Top-level const doesn’t influence a function signature
  15. Does “const” just mean read-only or something more?
  16. Why does “extern const int n;” not work as expected?
  17. C++ where to initialize static const
  18. When to use const and const reference in function args?
  19. Non-static const member, can’t use default assignment operator
  20. Why does C++ not have a const constructor?
  21. Calling a const function rather than its non-const version
  22. Why use a const member function?
  23. What are top-level const qualifiers?
  24. Pointer to array with const qualifier in C & C++
  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. Should I still return const objects in C++11? [duplicate]
  28. Returning non-const reference from a const member function
  29. How is its lifetime of a return value extended to the scope of the calling function when it is bound to a const reference in the calling function?
  30. Is it safe to make a const reference member to a temporary variable?

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