Checking for NULL pointer in C/C++

Question

In a recent code review, a contributor is trying to enforce that all NULL checks on pointers be performed in the following manner:

int * some_ptr;
// ...
if (some_ptr == NULL)
{
    // Handle null-pointer error
}
else
{
    // Proceed
}

instead of

int * some_ptr;
// ...
if (some_ptr)
{
    // Proceed
}
else
{
    // Handle null-pointer error
}

I agree that his way is a little more clear in the sense that it's explicitly saying "Make sure this pointer is not NULL", but I would counter that by saying that anyone who's working on this code would understand that using a pointer variable in an if statement is implicitly checking for NULL. Also I feel the second method has a smaller chance of introducing a bug of the ilk:

if (some_ptr = NULL)

which is just an absolute pain to find and debug.

Which way do you prefer and why?

Answer 1

In my experience, tests of the form if (ptr) or if (!ptr) are preferred. They do not depend on the definition of the symbol NULL. They do not expose the opportunity for the accidental assignment. And they are clear and succinct.

Edit: As SoapBox points out in a comment, they are compatible with C++ classes such as auto_ptr that are objects that act as pointers and which provide a conversion to bool to enable exactly this idiom. For these objects, an explicit comparison to NULL would have to invoke a conversion to pointer which may have other semantic side effects or be more expensive than the simple existence check that the bool conversion implies.

I have a preference for code that says what it means without unneeded text. if (ptr != NULL) has the same meaning as if (ptr) but at the cost of redundant specificity. The next logical thing is to write if ((ptr != NULL) == TRUE) and that way lies madness. The C language is clear that a boolean tested by if, while or the like has a specific meaning of non-zero value is true and zero is false. Redundancy does not make it clearer.