error: ‘NULL’ was not declared in this scope

Question

I get this message when compiling C++ on gcc 4.3

error: ‘NULL’ was not declared in this scope

It appears and disappears and I don\'t know w

Answer 1

GCC is taking steps towards C++11, which is probably why you now need to include cstddef in order to use the NULL constant. The preferred way in C++11 is to use the new nullptr keyword, which is implemented in GCC since version 4.6. nullptr is not implicitly convertible to integral types, so it can be used to disambiguate a call to a function which has been overloaded for both pointer and integral types:

void f(int x);
void f(void * ptr);

f(0);  // Passes int 0.
f(nullptr);  // Passes void * 0.