char holding a defined character literal value?This issue has been automatically converted from the original issue lists and some formatting may not have been preserved.
Authors: Derek M. Jones, WG14
Date: 1992-12-10
Reference document: X3J11/91-062
Submitted against: C90
Status: Closed
Converted from: dr.htm, dr_040.html
Refer to subclause 6.1.2.5, page 22, lines 32-36:
a.
char c = 7; /* implementation defined behavior, since 7 need not
be a member of the basic execution character set */
b.
c = 'a'; /* ok */
c++; /* implementation defined */
c.
c = '1'; /* ok */
c++; /* ok? */
It has been suggested that the above constructs are not implementation defined.
Subclause 6.1.3.4, page 29, lines 30-33:
d.
c = '\07'; /* what is in the source/execution character set is
given in subclause 5.2.1. Anything else is an extension. */
e.
c = '$';
It has been suggested that characters may be added to the basic source/execution character set without implementation defined behavior being invoked. (I guess my position on this item can be deduced from the text.)
Comment from WG14 on 1997-09-23:
a. Subclause 6.1.2.5 says “An object declared as type char is large enough to
store any member of the basic execution character set... If other quantities are
stored in a char object, the behavior is implementation-defined: the values
are treated as either signed or nonnegative integers.” Consider this example:
char c = 7;
The assignment c = 7 is not implementation-defined because, from a reasonable
reading of subclause 6.1.2.5, it is clear that the only implementation-defined
behavior here is the signedness of the value of the char object.
b. Another example:
c = 'a';
c++;
The increment of c after assigning an 'a' to it is defined by the
implementation because the numeric encoding of 'a' is defined by the
implementation. If 'a' were equal to CHAR_MAX, the increment could even
cause an overflow (cf. subclause 5.2.1).
c. Another example:
c = '1';
c++;
The increment of c after assigning a '1' to it is not implementation-defined
because the characters '0' through '9' are required to be a contiguous range
(cf. subclause 5.2.1). Thus, the result is '2'.
d. Another example:
c = '\07';
The value of the character constant '\07' is defined by the C Standard (cf.
subclause 6.1.3.4, page 29, line 10-13). The implementation-defined behavior of
some escape sequences, described on page 29, lines 30-33, is clarified in the
example on page 30, lines 8-14.
e. Another example:
c = '$';
If $ is in the execution character set, the value of '$' is locale-specific
and so must be defined by the implementation (cf. subclause 5.2.1).