Difference between NULL and NUL

Answer 1

NUL usually refers to the NUL device as used in CP/M, DOS and Windows. It is also an abbreviation for the null character ('\0'). NUL has no meaning with regards C/C++.

In C/C++, NULL is a symbol for the value zero (0x00000000 on 32-bit systems). All pointer variables must be initialised before they can be used. If a pointer is not in use, it must be zeroed (nullified).

Example:

#include <iostream>

using namespace std;

int main()

{

cout << "Command\t\tAddressOf (&p)\tPointsTo (p)\tValueAt (*p)" << endl;

cout << "-------\t\t--------------\t------------\t------------" << endl;

int * p; cout << "int * p;" << "\t0x" << &p << "\tN/A\t" << "\tN/A" << endl;

p = new int; cout << "p = new int;" << "\t0x" << &p << "\t0x" << p << "\t" << *p << endl;

*p = 12; cout << "*p = 12;" << "\t0x" << &p << "\t0x" << p << "\t" << *p << endl;

delete( p ); cout << "delete( p );" << "\t0x" << &p << "\t0x" << p << "\t" << *p << endl;

p = NULL; cout << "p = NULL;" << "\t0x" << &p << "\t0x" << p << "\tN/A" << endl << endl;

return( 0 );

}