What is meant with const at end of function declaration

Question

I got a book  where there is written something like   class Foo    public      int Bar int random arg  const                  code            What does it mean

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Bar is guaranteed not to change the object it is being invoked on  See the section about const correctness in the C   FAQ  for example

User · Answer

A  const function   denoted with the keyword const after a function declaration  makes it a compiler error for this class function to change a member variable of the class   However  reading of a class variables is okay inside of the function  but writing inside of this function will generate a compiler error     Another way of thinking about such  const function  is by viewing a class function as a normal function taking an implicit this pointer  So a method int Foo  Bar int random arg   without the const at the end  results in a function like int Foo Bar Foo  this  int random arg   and a call such as Foo f  f Bar 4  will internally correspond to something like Foo f  Foo Bar  amp f  4   Now adding the const at the end  int Foo  Bar int random arg  const  can then be understood as a declaration with a const this pointer  int Foo Bar const Foo  this  int random arg   Since the type of this in such case is const  no modifications of member variables are possible   It is possible to loosen the  const function  restriction of not allowing the function to write to any variable of a class  To allow some of the variables to be writable even when the function is marked as a  const function   these class variables are marked with the keyword mutable   Thus  if a class variable is marked as mutable  and a  const function  writes to this variable then the code will compile cleanly and the variable is possible to change   C  11   As usual when dealing with the const keyword  changing the location of the const key word in a C   statement has entirely different meanings   The above usage of const only applies when adding const to the end of the function declaration after the parenthesis    const is a highly overused qualifier in C    the syntax and ordering is often not straightforward in combination with pointers  Some readings about const correctness and the const keyword   Const correctness  The C    const  Declaration  Why  amp  How

User · Answer

Function can t change its parameters via the pointer reference you gave it   I go to this page every time I need to think about it   http   www parashift com c  -faq-lite const-correctness html  I believe there s also a good chapter in Meyers   More Effective C

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Similar to this question   In essence it means that the method Bar will not modify non mutable member variables of Foo

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Consider two class-typed variables   class Boo           Boo b0           mutable object const Boo b1     non-mutable object   Now you are able to call any member function of Boo on b0  but only const-qualified member functions on b1

User · Answer

I always find it conceptually easier to think of that you are making the this pointer const  which is pretty much what it does

[c++] What is meant with "const" at end of function declaration?

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