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Many programmers prefer to assign pointer variables to the null
pointer by using the
NULL macro:
class header {
public: link *first_link_pointer;
header ( ) {
first_link_pointer = NULL;
}
...
};
As explained in Segment 136, the C++ compiler replaces
the characters in macros before regular compilation begins.
Instances of the NULL macro, which happens to be declared
in the iostream.h header file, are replaced by 0.
By using NULL instead of 0, you identify the places where
0 is used as a special pointer, rather than as an ordinary
integer, thereby increasing program clarity.