Are NUL and NULL interchangeable in C? [duplicate]

Question

Just read pointer on C book by Kenneth Reek. It says that a NUL byte is one whose bits are all 0, written like this '\0' and NULL has a value 0 which refers to a pointer whose value is zero.

Both are integers and have the same value, so they could be used interchangeably.

and this code also:

char const *keyword[] = { "do", "for", "if", "register", 
                              "return", "switch", "while", NULL };

In this code, the NULL lets functions that search the table detect the end of the table. So, can we interchange NULL and NUL macros?

Answer 1

NUL is the notation for an ASCII character code 0.

NULL is a macro defined in stddef for the null pointer.

So, no, they are not to be used interchangeably.

Answer 2

There is no standardized NUL macro, at least not in C.

Also, NULL has the advantage over a plain 0 literal that it signals to the reader that "hey, we're dealing with a pointer" which might be considered an advantage.

In C++, the idiom was for a long while to just write 0, but then they seem to have reversed that and introduced a new literal, nullptr for some reason(s).

In C, I recommend writing NULL for pointers and '\0' for characters.