Many programmers routinely ignore compiler warnings. After all, if the problem were serious, it would be an error, right? This thinking may be relatively harmless in other languages, but in C++, it's a good bet compiler writers have a better grasp of what's going on than you do. For example, here's an error everybody makes at one time or another:

class B 
{
public:
    virtual void f() const;
};

class D : public B 
{
public:
    virtual void f();
};

The idea is for D::f to redefine the virtual function B::f, but there's a mistake: in B, f is a const member function, but in D it's not declared const. One compiler I know says this about that:

warning: D::f() hides virtual B::f()

Too many inexperienced programmers respond to this message by saying to themselves, "Of course D::f hides B::f — that’s what it’s supposed to do!" Wrong. This compiler is trying to tell you that the f declared in B has not been redeclared in D; instead, it's been hidden entirely (see Item 33 for a description of why this is so).

Things to Remember

• Take compiler warnings seriously, and strive to compile warning free at the maximum warning level supported by your compilers.
• Don't become dependent on compiler warnings, because different compilers warn about different things. Porting to a new compiler may eliminate warning messages you've come to rely on.