passing ‘const this argument discards qualifiers [-fpermissive]

Question

I have a class Cache which has a function write specified as

bool write(const MemoryAccess &memory_access, CacheLine &cl);

Answer 1

When you call a method via a pointer to an object, this object is implicitly passed to the method as this pointer. c probably has type const Cache*. Since method write is not declared as const, it has non-const this pointer accessible from its body requiring const qualifier of c to be discarded.

Answer 2

Also if your class's method returns pointer on any member you shouldn't forget write const before returning type example:

const float * getPosition() const{...}

Answer 3

Since c is of type const Cache *, you can only call const member functions on it.

You have two options:

(1) remove const from the declaration of c;

(2) change Cache::write() like so:

 bool write(const MemoryAccess &memory_access, CacheLine &cl) const;

(Note the added const at the end.)