C++ NULL vs nullptr

NULL is an implementation-defined macro that are consider problematic practice in C++.

Overloading

int f(int);
int f(int*);
 
f(NULL); // ambiguous

Worse:

int g(long);
int g(long*);
 
g(NULL); // guess who get called?

Optimization

A nullptr_t overload can be slightly fast than a pointer overload if we know a pointer is NULL at compile time.

https://godbolt.org/z/Y7xKb4

nullptr In C

• The proposal: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2394.pdf
• related: Type-generic macro
• “Conditional expressions such as (1 ? 0 : NULL) and (1 ? 1 : NULL) have different status depending how NULL is defined. Whereas the first is always defined, the second is a constraint violation if NULL has type void*, and defined otherwise”
• “A NULL argument that is passed to a va_arg function that expects a pointer can have severe consequences. On many architectures nowadays int and void* have different size, and so if NULL is just 0, a wrongly sized arguments is passed to the function.”