Issue 0050: Does a proper definition of wchar_t need to be in scope to write a wide-character literal?

This issue has been automatically converted from the original issue lists and some formatting may not have been preserved.

Authors: C. Breeus, Project Editor (P.J. Plauger)
Date: 1993-02-24
Submitted against: C90
Status: Closed
Cross-references: 0017.07
Converted from: dr.htm, dr_050.html

Subclause 6.1.3.4 says that the type of a wide character constant is wchar_t, and subclause 6.1.4 says the type of a wide character string is array of wchar_t.

Subclause 7.1.6 says the typedef name wchar_t must be defined in <stddef.h>.

Question: When a compiler sees a literal of the form L'...' or L"..." must it not check that

1. The name wchar_t is visible at that place.
2. The name is a typedef name. It could be redefined in an inner scope.
3. It is a typedef for an integral type. Again, it could be redefined.

And then, take that integral type as the meaning of wchar_t. I suppose it cannot just hope for the best and take a type that makes it feel good.

Comment from WG14 on 1997-09-23:

Response

A similar issue was explained in response to Defect Report #017 Question 7, regarding size_t. The relevant citation here is from subclause 6.1.3.4, page 29, lines 36-37:

A wide character constant has type wchar_t, an integral type defined in the <stddef.h> header.

The intent of this sentence is to note that a wide character constant has an integral type. That integral type is the same integral type used to define wchar_t in the header <stddef.h>. The sentence imposes no requirement that this particular definition of wchar_t be in scope wherever you write a wide character constant. It certainly does not suggest that the translator should honor any other definition of wchar_t that may be in scope, as the type for a wide character constant.

Rather, the sentence suggests that the translator knows what integral type to assign to a wide character constant. The implementation further knows to define wchar_t within the header <stddef.h> as having that same integral type. Thus, the program has a way of obtaining a name for this type, if it chooses - by including the header <stddef.h>. But it need not invoke that mechanism just to assist the translator.

It is an unfortunate, but widespread, practice within the C Standard to use abbreviated language for describing some types. Thus, subclause 6.1.4, page 31, lines 5-6 say:

for wide string literals, the array elements have type wchar_t, ...

instead of the more long winded (but clearer):

for wide string literals, the array elements have the same type used to define wchar_t in the header <stddef.h>, ...

We feel the usage is sufficiently uniform that the meaning intended by the Committee is sufficiently clear, even as we acknowledge that the words can be (and have been) misread.

So to put the matter crassly, the translator does “just hope for the best and take a type that makes it feel good,” as you conjectured.