dinapoli@rodan.acs.syr.edu (Ron DiNapoli) (05/09/90)
A few weeks back I posted a message regarding a problem I was having with
the MPW 3.0 C pre-processor. This problem reared its ugly head when I at-
tempted to port my MPW 2.0 C code to 3.0. The majority of responses I re-
ceived advised me to upgrade to MPW C 3.1. I did this, but the problem
did not go away. Well I finally discovered what was going wrong... I had the
following macro defined:
#define OP(tkdef,tkname,d1,d2) {#tkdef,tkname,d1,d2}
and I wanted to expand the following:
OP(TK_SSLASH,"//",ASSC_YFX,400)
Anybody see the problem? In MPW C 3.0 and later, the '//' symbol stands
for a comment. It also seems that the preprocessor is unable to detect
that this particular comment character is occurring within a string.
Since it doesn't, the preprocessor sees the open end of a string, and never
finds the closing " (because the real one was 'commented' out) before its
internal buffer overflows. Once discovered, the fix was easy. I just
changed this particular occurrance of OP to:
OP(TK_SSLASH,"/\/",ASSC_YFX,400)
So, it this a bug? In my opinion it isn't. Take for example the following
macro definition:
#define PRINTIT(prstr) printf("PRINTIT has been called with: %s\n",prstr);
and the following program:
main()
{
PRINTIT("/* This is a comment */")
PRINTIT(" This is normal text ")
PRINTIT(" // Another type of comment")
}
The preprocessor (3.1 C) will output the following:
main()
{
printf("PRINTIT has been called with: %s\n","");
printf("PRINTIT has been called with: %s\n"," This is normal text ");
Obviously, it was unable to finish expanding the last macro because of the
// comment character. Attempting to further compile this example will
NOT work!
Note how in the first occurrance of the PRINTIT macro, the text between the
/* */ comment characters does not appear. This tells me that in the 3.0/3.1
C preprocessor, comments are "taken out" regardless of where they appear.
Thus my problems with the '//' in my string seems consistent with this
philosophy. For this reason, I would say it is not a bug at all!
Ron D.dierks@ndcvb.cc.nd.edu (Timothy Dierks) (05/10/90)
From article <3238@rodan.acs.syr.edu>, by dinapoli@rodan.acs.syr.edu (Ron DiNapoli): > Anybody see the problem? In MPW C 3.0 and later, the '//' symbol stands > for a comment. It also seems that the preprocessor is unable to detect > that this particular comment character is occurring within a string. > > Note how in the first occurrance of the PRINTIT macro, the text between the > /* */ comment characters does not appear. This tells me that in the 3.0/3.1 > C preprocessor, comments are "taken out" regardless of where they appear. And he quoteth from the book of Kernighan and Ritchie, Appendix A, Section A2.2: The characters /* introduce a comment, which terminates with the characters */. Comments do not nest, and they do not occur within string or character literals. Here endeth the lesson. Tim Dierks dierks@ndcvb.cc.nd.edu Go Irish! Only >11< days to those silly hats.
philip@Kermit.Stanford.EDU (Philip Machanick) (05/10/90)
In article <3238@rodan.acs.syr.edu>, dinapoli@rodan.acs.syr.edu (Ron DiNapoli) writes: > ... advised me to upgrade to MPW C 3.1. I did this, but the problem > did not go away. Well I finally discovered what was going wrong... I had the > following macro defined: > > #define OP(tkdef,tkname,d1,d2) {#tkdef,tkname,d1,d2} > > and I wanted to expand the following: > > OP(TK_SSLASH,"//",ASSC_YFX,400) > > Anybody see the problem? In MPW C 3.0 and later, the '//' symbol stands > for a comment. It also seems that the preprocessor is unable to detect > that this particular comment character is occurring within a string. > Since it doesn't, the preprocessor sees the open end of a string, and never > finds the closing " (because the real one was 'commented' out) before its > internal buffer overflows. Once discovered, the fix was easy. I just > changed this particular occurrance of OP to: > > OP(TK_SSLASH,"/\/",ASSC_YFX,400) > > > So, it this a bug? In my opinion it isn't. Take for example the following > macro definition: [example deleted] > Note how in the first occurrance of the PRINTIT macro, the text between the > /* */ comment characters does not appear. This tells me that in the 3.0/3.1 > C preprocessor, comments are "taken out" regardless of where they appear. > Thus my problems with the '//' in my string seems consistent with this > philosophy. For this reason, I would say it is not a bug at all! From Kernighan and Richie (2nd edition; p. 192): " Comments do not nest, and they do not occur within string or character literals. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ " ^^^^^^^^^^^^^^^^^^ I haven't checked the behaviour you reported, but if MPW C 3 behaves as you suggest it does, this IS a bug. Philip Machanick philip@pescadero.stanford.edu