C/C++ Macro for null safe pointer access

Question

I want to write a C/C++ macro for null safe pointer access. I currently have this, which works well:

#define NULL_SAFE(p, e) if (p) p->e
NULL_SAFE(myPtr, myMethod(myArg));

But what I really want is to have something like this:

NULL_SAFE(
  myPtr, myMethod(myArg),
  myOtherPtr, myOtherMethod(myOtherArg),
  yetAnotherMyPtr, plsStopMethod(grArg),
  ...
);

which would expand to:

  if (myPtr) myPtr->myMethod(myArg);
  if (myOtherPtr) myOtherPtr->myOtherMethod(myOtherArg);
  if (yetAnotherMyPtr) yetAnotherMyPtr->plsStopMethod(grArg);

I can think of a whole bunch of these I might like to use, but they all operate on the same concept as this.

Is this possible? Does this already exist somewhere? Any suggestions? Thanks for your help!

Answer 1

If the NULL check is part of an algorithm, then just type out the NULL check explicitly without any icky macros.

If the NULL check is a way of defensive programming, the correct way to do this is assert(ptr);. If the assert ever triggers, go fix the bug that caused it. Repeat until there are no bugs left, then remove the assert from the production-quality code.

Answer 2

C++11:

inline void null_safe()
{
}

template <typename Ptr, typename Fn, typename... Args>
void null_safe(Ptr&& ptr, Fn&& fn, Args&&... args)
{
    if (ptr)
        fn();
    // you could put "else" here                                                                                                            
    null_safe(std::forward<Args>(args)...);
}

You can use any callable as the second argument, so:

int f2() {
    return printf("f2\n");
}

int f3() {
    return printf("f3\n");
}

int main()
{
    int i1 = 1;

    null_safe(
        &i1, f2
        );

    null_safe(
        NULL, f2,
        &i1, f3
        );
}

You can also use any predicate as the first argument.

Why it's NULL there and not nullptr is left as an exercise for the reader.