Design by Contract in C++?

Question

Is that any library that aids in implementing design by contract principle in c++ application. EDIT:

Looking for much better than ASSERT something like this

Answer 1

Simplest?

Assert statements at the start of your function to test your requirements. Assert statements at the end of your function to test your results.

Yes, it's crude, its not a big system, but its simplicity makes it versatile and portable.

Answer 2

assert.h

Answer 3

I followed the teachings of the following articles:

An exception or a bug? (Miro Samek)

Simple Support for Design by Contract in C++ (Pedro Guerreiro)

What I ultimately applied was very much Samek's approach. Just creating macros for REQUIRE, ENSURE, CHECK and INVARIANT (based on the existing assert macro) was very useful. Of course it's not as good as native language support but anyway, it allows you to get most of the practical value from the technique.

As for libraries, I don't think that it pays to use one, because one important value of the assertion mechanism is its simplicity.

For the difference between debug and production code, see When should assertions stay in production code?.

Answer 4

Hi,

Some design patterns, such as the non-virtual interface make it natural to write pre/post-conditions for a given method:

#include <cassert>

class Car {
    virtual bool engine_running_impl() = 0;
    virtual void stop_impl() = 0;
    virtual void start_impl() = 0;

    public:
    bool engine_running() {
        return engine_running_impl();
    }

    void stop() {
        assert(engine_running());
        stop_impl();
        assert(! engine_running());
    }

    void start()
    {
        assert(! engine_running());
        start_impl();
        assert(engine_running());
    }
}


class CarImpl : public Car {
    bool engine_running_impl() {
        /* ... */
    }

    void stop_impl() {
        /* ... */
    }

    void start_impl() {
        /* ... */
    }
}