What header defines NULL in C++?

Question

According to C++ primer, header defines NULL. cpluspplus says it is defined in .

Ultimately, if

Answer 1

It is defined in

The C++11 standard section 18.2, table 30 explains what's in It says:

Table 30 — Header synopsis

Macros: NULL [...]

[...] The macro NULL is an implementation-defined C++ null pointer constant in this International Standard