mod.std.c Digest V6#12

[Orlando Sotomayor-Diaz]

From: Orlando Sotomayor-Diaz (The Moderator) <cbosgd!std-c>


mod.std.c Digest            Thu, 23 May 85       Volume 6 : Issue  12 

Today's Topics:
                           string literals
                         Undefined structures
----------------------------------------------------------------------

Date: Thu, 23 May 85 00:23:41 PDT
From: ucbvax!geacc022%timevx at cit-hamlet.arpa
Subject: string literals
To: cbosgd!std-c at BERKELEY

decvax!duke!george at idis's proposal:

>	string-literal:
>		unit-string-literal
>		string-literal unit-string-literal
>		string-literal character-constant

If you implement this, please add:

		character-constant string-literal

so that both

printf("string" '\n');	    /* would become printf("string\n");     */
printf('>' "message");	    /* he wants printf(">message");	    */

are allowed.  I think this fits in well with the string concatenation
already added, but it fits into the category of "Nice idea, but not
worth the trouble to implement" since you can use double quotes instead
of singles and get the desired effect (at the cost of a null byte).
Or is there a situation where the single quotes are needed?

			Gary Ansok
			GEACC022%TIMEVX @ CIT-HAMLET.ARPA
			GEA @ CALTECH.BITNET
			...ucbvax!cithep!timevx#geacc022

[ Just to keep the record straight, the latest draft (85-045, 4/30/85)
describes (C.1.4, p. 20-1) the string literal syntax as:

	string-literal:
		"s-char-sequence   "
				opt

	s-char-sequence:
		s-char
		s-char-sequence s-char

	s-char:
		any character in the source character set except the
			double-quote ", backslash \, or new-line character
		escape-sequence

It then adds the following:

Description

	A string literal is a sequence of zero or more characters 
enclosed in double-quotes, as in "xyz".

Constraints

	A new-line character must not appear in a string literal. The
single-quote ' is represented by itself or by the escape sequence \',
but the double-quote " must be represented by the escape sequence \";
in addition, the same escape sequences as described for character
constants may be used.

Semantics

	A string literal has static storage duration and type "array
of const char," and is initialized with the given characters.
String literals that are adjacent tokens are concatenated into
a single string literal.  A NUL character '\0' is then appended.

	Identical string literals need not be distinct.  A string literal
is not modifiable.

			-- Mod --

PS. To promote more up to date contributions to this group and to
the Committee, there will be a limited number of copies of the
new draft to be distributed.  However, I would like to stress that
our effort in distributing this should be compensated by you reading
it and sending comments to this group and/or members of the committee.
Send mail to the moderator and include a line with postal information
in the following format:

usmail:your name:address line 1:address line 2:address line 3:address line 4

i.e., no more than 5 colons should appear on your address line.  The
tag usmail:  is required, as shown above.  Larry Rosler agreed to
help on this distribution, so DON'T send mail to him requesting a copy.
There are no plans to make the draft available in electronic form.  ]


------------------------------

Date: Thu, 23 May 85 12:50:15 edt
From: Alan T. Bowler [SDG] <ihnp4!watmath!atbowler>
Subject: Undefined structures
To: std-c at cbosgd

Is the following program in error?  I realize that PCC and other
compilers will accept it without complaint, furthermore there
does exist code that depends on this "feature".  My feeling is that
such code came into existence by accident and the authors would
have not made the error if the compiler had of pointed out the problem.

    typedef struct {
    	int val;
    	struct st *y;
    } st;
    
    main() {
    	st *p = 0;
    	printf("OOPs\n", p);
    }

There are 2 problems here.  The first is that the name "st" is used
with 2 different meanings in this program.  First as a structure tag
and then as a typedef name.  I can accept this, but is there a clear
statement in the standard that structure tags and typedef names
are in independent scopes.  K&R is a little vague on this.
  The second problem is that by the end of the file (compilation unit,
module....) the struct with tag "st" is undefined.  I realize that
it must be possible to declare a pointer to a currently undefined structure
type in order that you can build self referencing structures, and mutually
referencing structures.  However, shouldn't these be resolved by the
end of the program?

------------------------------

End of mod.std.c Digest - Thu, 23 May 85 20:40:52 EDT
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