CODEWITHSUNDEEP
c++this-pointer
Sebastian Mach
Sebastian Mach

Reputation: 39089

If `this` is not const, why can't I modify it?

In The this pointer [class.this], the C++ standard states:

The type of this in a member function of a class X is X*.

i.e. this is not const. But why is it then that 

struct M {
    M() { this = new M; }
};

gives

error: invalid lvalue in assignment  <-- gcc
'=' : left operand must be l-value   <-- VC++
'=' : left operand must be l-value   <-- clang++
'=' : left operand must be l-value   <-- ICC
(source: some online compiler frontends)

In other words, this is not const, but it really is!

Upvotes: 25

Views: 672

Answers (1)

Sebastian Mach
Sebastian Mach

Reputation: 39089

Because in the same paragraph, it is also mentioned that this is a prvalue ("pure rvalue").

Examples mentioned in the standard for pure rvalue are the result of calling a function which does not return a reference, or literals like 1, true or 3.5f. The this-pointer is not a variable, it's more like a literal that expands to the address of the object for which the function is called ([class.this]). And like e.g. literal true has type bool and not bool const, this is of type X* and not X*const.

Upvotes: 45

Related Questions