http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52185
Bug #: 52185 Summary: Const member function may change the object for which the function is called. Classification: Unclassified Product: gcc Version: 4.7.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ AssignedTo: unassig...@gcc.gnu.org ReportedBy: lsoltys...@gmail.com According to paper www.open-std.org/JTC1/SC22/WG21/docs/papers/2011/n3242.pdf ( class.this point 2), a const member function shall not modify the object for which the function is called. With basic cases it is true, so for below class g++ returns error ('error: increment of member ‘A::a’ in read-only object'). class A { int a; public: int fun() const { a++; } }; Problems start when class contains references. In below example, const member function allows to change internal state of class A instances. This shouldn't be allowed. In my opinion compilation should failed, but g++ 4.7.0 doesn't report any problem. class A { int a1; int & a2; public: A() : a2(a1) { } int fun() const { a2++; } };