How compiler know about const member function

When you add const to a member function what you're doing is telling the compiler to reject your code if you try and modify any data in the object (with the odd exception, e.g. mutable). So the compiler has to do a bit of checking to see that the function really doesn't modify anything.

Unlike virtual functions, exception handling and runtime type information, const is one of those things that never makes it out of the back-end of the compiler [1]. The compiler doesn't add code to enforce "constness," it just checks as it compiles and if the code breaks the rules it rejects it. After compilation [1] there's no record in the object code that a function's const - and this is why you can do disgusting things in C++ with pointers at runtime.

Just to add to SA's references above, if you can find a copy, have a read of Inside the C++ object model by Stanley Lippman. It covers the program entities that make it through to the final machine code (e.g. virtual functions, RTTI) and what gets dumped during compilation (e.g. classes, attributes of data members, access specifiers).

[1] Strictly after linking - before then you might be able to work out a function's const from it's decorated name. If you do that they you have too much time on your hands!