How to ensure that every method of a class calls some other method first?

Question

I have :

class Foo {    public:       void log() { }        void a() {          log();       }        void b() {          log();       } }; 

Is there a way that I can have each method of Foo, call log(), but without me having to explicitly type log() as the first line of each function ? I want to do this, so that I can add behaviour to each function without having to go through each function and make sure the call is made, and also so that when I add new functions, the code is automatically added...

Is this even possible ? I can't imagine how to do this with macro's, so not sure where to begin... The only way I have thought of so far, is to add a "pre-build step", so that before compiling I scan the file and edit the source code, but that doesn't seem very intelligent....

EDIT: Just to clarify - I don't want log() to call itself obviously. It doesn't need to be part of the class.

EDIT: I would prefer using methods that would work cross platform, and using only the stl.

Answer 1

Thanks to the unusual properties of operator ->, we can inject code before any member access, at the expense of a slightly bent syntax:

// Nothing special in Foo struct Foo {     void a() { }     void b() { }     void c() { } };  struct LoggingFoo : private Foo {     void log() const { }      // Here comes the trick     Foo const *operator -> () const { log(); return this; }     Foo       *operator -> ()       { log(); return this; } }; 

Usage looks as follows:

LoggingFoo f; f->a(); 

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