Issue 1035: wctrans_t and wctype_t as nullptr_t

Authors: Jay Ghiron
Date: 2026-03-24
Submitted against: C23
Status: Open

No wording exists currently to say that wctrans_t and wctype_t cannot be defined as nullptr_t:

The types declared are wint_t described in 7.31.1;

wctrans_t

which is a scalar type that can hold values which represent locale-specific character mappings; and

wctype_t

which is a scalar type that can hold values which represent locale-specific character classifications.

(C23 7.32.1 "Introduction" paragraph 2.)

Before C23 nullptr_t did not exist as a scalar type so wctrans_t and wctype_t could not be defined as nullptr_t, but in C23 nullptr_t was added as a scalar type which is what wctrans_t and wctype_t are defined in terms of. An example of where this matters is:

#include<wctype.h>
int main(){
bool b=true;
wctrans_t t=b?wctrans("example"):0;
}

If wctrans_t were defined as nullptr_t, then this program would have a constraint violation:

One of the following shall hold for the second and third operands:

• both operands have arithmetic type;
• both operands have compatible structure or union type;
• both operands have void type;
• both operands are pointers to qualified or unqualified versions of compatible types;
• both operands have nullptr_t type;
• one operand is a pointer and the other is a null pointer constant or has type nullptr_t; or
• one operand is a pointer to an object type and the other is a pointer to a qualified or unqualified version of void.

(C23 6.5.16 "Conditional operator" paragraph 3.)

There seems to be no reason to allow for wctrans_t or wctype_t to be defined as nullptr_t. Such definitions would also not be sufficient to include all of the standard categories which are defined. The same is also true for bool, bit-precise integer types with a small width, and extended integer types with a small width.

Suggested correction

Modify C23 7.32.1 paragraph 2:

wctrans_t

which is a scalar type that can hold at least two nonzero values which represent locale-specific character mappings; and

wctype_t

which is a scalar type that can hold at least twelve nonzero values which represent locale-specific character classifications.

Note: Zero is already used to mean null for pointer types, though that is never clearly defined.