In addition to the paragraphs quoted in the question, there is paragraph 6.4.4.5/3: The keywords false and true are constants of type bool with a value of 0 for false and 1 for true. and 6.6/7: An identifier that is: […] — a predefined constant; […] is a named constant That makes false a named … Read more
Ordered comparison between a pointer and an integer is ill-formed in C++ (even when the integer is a null pointer constant such as it is in this case). The risk is that compilers are allowed to, and do, refuse to compile such code. You can rewrite it as either of these: if(myPtr != nullptr) if(myPtr)
I read (part of) the C99 standard to clear my mind. I found the sections that are of interest for my own question and I’m writing this as a reference. DISCLAIMER I’m an absolute beginner, 90% or more of what I have written is wrong, makes no sense, or may break you toaster. I also … Read more
Both (a) and (b) result in undefined behavior. It’s always undefined behavior to call a member function through a null pointer. If the function is static, it’s technically undefined as well, but there’s some dispute. The first thing to understand is why it’s undefined behavior to dereference a null pointer. In C++03, there’s actually a … Read more
A message sent to a nil object is perfectly acceptable in Objective-C, it’s treated as a no-op. There is no way to flag it as an error because it’s not an error, in fact it can be a very useful feature of the language. From the docs: Sending Messages to nil In Objective-C, it is … Read more
int* ptr = NULL; //Is this going to avoid the problem This will cause ptr to point to NULL which you can explicitly check for as a default/uninitialized value. It prevents the problem you describe, but a careless programmer can still accidentally dereference a null pointer without checking, causing undefined behaviour. The main advantage is … Read more
In C, a void* can be implicitly converted to any T*. As such, making NULL a void* is entirely appropriate. But that’s profoundly dangerous. So C++ did away with such conversions, requiring you to do most pointer casts manually. But that would create source-incompatibility with C; a valid C program that used NULL the way … Read more
The two concepts are orthogonal: A void pointer, (void *) is a raw pointer to some memory location. A null pointer is a special pointer that doesn’t point to anything, by definition. It can be a pointer to any type, void or otherwise. A void pointer can be null or not: void *void_ptr1 = nullptr; … Read more
The object foo is a local variable with type Foo*. That variable likely gets allocated on the stack for the main function, just like any other local variable. But the value stored in foo is a null pointer. It doesn’t point anywhere. There is no instance of type Foo represented anywhere. To call a virtual … Read more
I always think simply if(p != NULL){..} will do the job. It will.