mason@tc.fluke.COM (Nick Mason) (07/07/90)
What should sscanf do with the following? Does anyone
have the ANSI standard and shed some light on the following?
I would like "hard" replies, not "I think it should ....".
Thanks in advance.
Given:
char *buf="123";
char *str="123x";
int a, b, x;
b = -99;
x = sscanf(str, "%d%n", &a, &b);
printf("x=%d, a=%d, b=%d\n",x,a,b);
x = sscanf(buf, "%d%n", &a, &b);
printf("x=%d, a=%d, b=%d\n",x,a,b);
What is the CORRECT output according to the standard???
I tried this with 3 different compilers and got the following:
compiler A:
x=1 a=123 b=3
x=1 a=123 b=3
compiler B:
x=1 a=123 b=3
x=1 a=123 b=4 <-- yes 4.
compiler C:
x=1 a=123 b=3
x=1 a=123 b= -99
I'm confused????!!!!! Compiler C is "100% ANSI compatible".????
Nick.daniels@tle.enet.dec.com (Bradford R. Daniels) (07/07/90)
> compiler A: > x=1 a=123 b=3 > x=1 a=123 b=3 This is the correct result. > compiler B: > x=1 a=123 b=3 > x=1 a=123 b=4 <-- yes 4. This is clearly wrong, since there aren't even 4 characters in the string... > compiler C: > x=1 a=123 b=3 > x=1 a=123 b= -99 This is also wrong, since %n does not consume any input, and so the lack of input should not cause it to fail. > I'm confused????!!!!! Compiler C is "100% ANSI compatible".???? ANSI compatible does not mean bug free. This behavior is a bug, and I think I see how it's happening... In fact, I think I'll go make sure my RTL doesn't have the same problem... - Brad ----------------------------------------------------------------- Brad Daniels | Digital Equipment Corp. almost DEC Software Devo | definitely wouldn't approve of "VAX C RTL Whipping Boy" | anything I say here...
kdq@demott.COM (Kevin D. Quitt) (07/08/90)
In article <1990Jul6.181830.2549@tc.fluke.COM> mason@tc.fluke.COM (Nick Mason) writes: > >I tried this with 3 different compilers and got the following: > >compiler A: > > x=1 a=123 b=3 > x=1 a=123 b=3 > >compiler B: > > x=1 a=123 b=3 > x=1 a=123 b=4 <-- yes 4. > >compiler C: > > x=1 a=123 b=3 > x=1 a=123 b= -99 > I'm confused by example C: where did it get the old value of b? BTW, Microsoft C and cc on Motorola Delta 3x00 agree with A, and gnu's gcc coredumps. -- _ Kevin D. Quitt demott!kdq kdq@demott.com DeMott Electronics Co. 14707 Keswick St. Van Nuys, CA 91405-1266 VOICE (818) 988-4975 FAX (818) 997-1190 MODEM (818) 997-4496 PEP last 96.37% of all statistics are made up.
gwyn@smoke.BRL.MIL (Doug Gwyn) (07/08/90)
In article <1990Jul6.181830.2549@tc.fluke.COM> mason@tc.fluke.COM (Nick Mason) writes: > int a, b = -99, x; > x = sscanf("123x", "%d%n", &a, &b); > printf("x=%d, a=%d, b=%d\n",x,a,b); > x = sscanf("123", "%d%n", &a, &b); > printf("x=%d, a=%d, b=%d\n",x,a,b); >What is the CORRECT output according to the standard??? You've uncovered an interesting feature: Although the %n specifier does not consume input, it can still have an "input failure" when EOF was encountered during preceding conversions that matched non- empty sequences. >compiler C: > x=1 a=123 b=3 > x=1 a=123 b= -99 >I'm confused????!!!!! Compiler C is "100% ANSI compatible".???? It might be; it did return the right answer in this particular case. P.S. This is not an official interpretation; if it bothers you, please send an official request for interpretation to CBEMA X3.
inst182@tuvie (Inst.f.Techn.Informatik) (07/10/90)
To add a new variant, on a DECstation 3100 (Ultrix 2.1) both cc (1.31) and gcc (1.37) give the following results: x=2, a=123, b=3 x=1, a=123, b=3 (no coredumps)