Question

Is there a difference between using const:

Cannot change the datatype but can change the value of a or b

int add(const int a, const int b); 

Can change the datatype but cannot change the value of a or b

int add(int const a, int const b); 

Cannot change the datatype and cannot change the value of a or b

int add(const int const a, const int const b); 

Many thanks for any suggestions

Answer 1

I don’t know how one is supposed to changed the datatype of a variable in C++ …

‘const’ is a promise you make to the compiler about not modifying a value. It complains when you don’t (probably uncovering z bug in the process). It also helps it to do various optimizations.

Here are some const examples and what they mean :

f ( const int a  ) 

f cannot change the value of ‘a’.

f ( int const a ) 

the same but written in a weird way

f ( const int const a ) 

means nothing, gcc tells me ‘duplicate const’

f ( const int * pa ) 

f cannot change the value pointed to by pa

f ( int * const pa ) 

f cannot change the value of the pointer

f ( const int * const pa ) 

f cannot change the value of the pointer nor the value pointed to

f ( int a ) const  

The member function f cannot modify its object

Hope it makes things clearer ..