Why do we have nullptr but not nullchar?

Question

My understanding - and I'm sure I'm about to learn - is that nullptr was added to C++ to formalise the convention that a zero value for a pointer means the pointer does not point to a valid object. Is there a case for (or against) adding a corresponding nullchar to formalise the convention that a zero value for a char means the char is not a valid character but is instead the terminator of a string? I can see a few things which the two cases have in common:

Type safety: 0 can have several different types, so it's easy to mistakenly assign a non-pointer variable to zero instead of the pointer variable you meant to. It's also easy to call the wrong overloaded function if you get it just right. Having a special and strongly-typed value prevents this kind of mistake, and this could be true for char types as well.

Expressiveness: Assigning a variable to be nullptr makes it clear to the reader that the variable is a pointer (because only a pointer can be assigned to that value) and that it points to no object. Assigning a char to nullchar would add the same kind of clarity and readability.

There's more, but I'm sure you get the idea. So why do we have nullptr but not nullchar?

If you want, you can make it yourself! Put this in one of your 'global' headers: `static inline constexpr char nullchar = '\0';`. — Adrian Mole, Nov 01 '20 at 20:55
@Enrico -- www.google.com is very cromulent for figuring out what cromulent means. — Sam Varshavchik, Nov 01 '20 at 20:58
I expected to find it on [WordReference](https://www.wordreference.com/definition/cromulent), but it's not there, so I didn't search with google, thinking it could be a typo. However, thanks for pointing me to the Simpsons. — Enlico, Nov 01 '20 at 21:00
Can you please give examples in your question reenforcing why you think a nullchar is a good idea? I personally don't see a need — hookenz, Nov 01 '20 at 21:01
`\0` terminates c strings or string literals, but not a `std::string`. The `\0` is a valid character in a `std::string` and could occur at any position. — t.niese, Nov 01 '20 at 22:56
@Eljay But 0 is a valid value for a pointer as well. Both pointers and chars give a special meaning to this one value. — bythescruff, Nov 02 '20 at 00:12
Pointers give special meaning to zero. Chars do not give special meaning to zero. — Eljay, Nov 02 '20 at 13:08

score 2 · Accepted Answer · answered Nov 01 '20 at 20:55

No, because there's not as much reason to, really. nullptr was added to remove the need of the NULL macro, which in C is defined as something like (void*)0. In C, void* is implicitly convertible to any pointer type, so this would work. However, this is not true in C++, which removed this implicit convertibility (but not its inverse, from any pointer type to void*), to increase type safety. However, C++ still wanted to have an easy way to make any pointer a null pointer, which is why nullptr_t was introduced, which is implicitly convertible to any pointer type like void* once was, BUT can only contain the null pointer value, nullptr. In C++ you can represent a null character with '\0' with no type ambiguity or unnecessary explicit conversions, so there's no reason for a nullchar value, which would also take up another valuable reserved identifier (standard committee really likes to preserve those.)

"_In C, void* is implicitly convertible to any pointer type, so this would work._" No, it works by definition. — curiousguy, Nov 01 '20 at 21:08
Aha! The fact that pointers have different types is the key point I was overlooking. Thanks. — bythescruff, Nov 02 '20 at 00:14

Why do we have nullptr but not nullchar?

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