NULL vs. nullptr: Why Was C 's Null Pointer Representation Changed?

NULL vs. nullptr: The Evolution of Null Pointer Representation

In C 0x, the traditional NULL macro was replaced by nullptr. This change was not merely cosmetic; it introduced significant improvements to the language's handling of null pointers.

Why the Replacement?

NULL, defined as 0, created a potential ambiguity in overloaded function resolution. Consider the following code:

void f(int);
void f(foo *);

If a call to f(NULL) is made, the compiler is unsure whether to invoke f(int) or f(void *). This ambiguity is resolved by using nullptr, which has type std::nullptr_t and is implicitly convertible to any pointer type.

Benefits of nullptr

Compared to NULL, nullptr offers several advantages when working with pointers:

• Overload Resolution Clarity: As mentioned above, nullptr avoids the ambiguity in function overload resolution, ensuring that the correct function signature is selected.
• Type Safety: nullptr cannot be implicitly converted to integer types or other irrelevant types, preventing potential conversion errors.
• Consistency: nullptr provides a consistent representation of null pointers across C platforms and compilers, eliminating potential cross-compilation issues.

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