Question

I’ve noticed that g++ is smart enough to identify when a function is returning a pointer to a temporary/local variable, e.g.

int *foobar()
{
      int a;
      return &a;
}

Will result in:

 warning: address of local variable ‘a’ returned

Is there a way that I can define a function prototype to only accept pointers that the compiler can tell are not temporary. So lets say I have a function

 barfoo(int *a_int);

Is there a way I can tell g++ to complain if someone passes a pointer to a local/temporary object into it? This would prohibit people from calling barfoo with invalid pointers and potentially save debugging some annoying issues.

Example:

   void barfoo(int *a)
   {
        cerr << a << endl;
   };

   void foobar()
   {
        int a;
        barfoo(&a);
   }

I would like the compiler to complain about the `barfoo(&a)’.

Answer 1

I don’t think there is any way to get the compiler to enforce it, but you can detect some instances earlier by using malloc_size.

void someFunc(int * mustBeHeap) {
   assert(0!=malloc_size(mustBeHeap));
   //do stuff
}

Unfortunately you will get false positives from code like this:

void someOtherFunc() {
    int * myInts=(int *)malloc(sizeof(int)*20);
    someFunc(&(myInts[3]));
}

It won’t work too well with anything allocated with new, boost::pool, etc. In fact, you will get false positives from just about everything.

Also, malloc_size is non-standard.

Edit:

After looking at one of your comments above about taking ownership, it looks like some of the things I described as false positives are in fact situations you also want to detect since you intended to free the memory from the pointer.