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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: Abstract Syntax Tree for C programs
Date: Tue, 04 Jun 2019 14:37:10 -0700
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James Kuyper <jameskuyper@alumni.caltech.edu> writes:
[...]
> Constants are things like 'a', 5, 6.0. Such initializers are not
> required to be constants, they only have to be constant expressions.
> 1<<31 meets all of the requirements for a valid integer constant
> expression.

No, it doesn't (if INT_MAX <= 2147483647).  N1570 6.6p4, under
Constraints:

    Each constant expression shall evaluate to a constant that is
    in the range of representable values for its type.

(I find the use of the word "constant" slightly problematic, since it
doesn't refer to the syntactic category "constant", but the meaning is
clear enough.)

One could argue either that 1<<31 is not a constant expression,
or that it is a constant expression but it violates a constraint,
but either way the requirement is the same: a diagnostic message
is required if it's used in a context that requires a constant
expression.  For example rand() also meets the *syntactic* definition
of a constant-expression, but it violates the constraint in 6.6p3.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */