mnc@m10ux.UUCP (04/27/87)
Here is a nasty little bug I just ran into with the Sys V R2 (VAX) C
compiler and the Sun C compiler (but it does not exist on 4.3 BSD).
Consider:
extern void f(), (*fp)();
int x;
main() {
g(x ? f : fp);
g(x ? f : *fp);
}
Both of the uses of the "? :" operator produce the message "operands of
: have incompatible types". Changing "void" to any other type makes
both error messages go away. Notice that there is no attempt to use
a void value in the above expression. Since this code is likely to
occur in any C program that passes procedures (i.e. void functions) as
arguments, I don't understand how the bug could have persisted this long.
The only work-around I can think of (besides changing the declaration of
f and fp) is to use "if - else" instead of "? - :".
--
Michael Condict {ihnp4|vax135|cuae2}!m10ux!mnc
AT&T Bell Labs (201)582-5911 MH 3B-416
Murray Hill, NJdave@runx.ips.oz (Dave Horsfall) (05/05/87)
cur in any C program that passes procedures (i.e. void functions) as > arguments, I don't understand how the bug could have persisted this long. > The only work-around I can think of (besides changing the declaration of > f and fp) is to use "if - else" instead of "? - :". > -- > Michael Condict {ihnp4|vax135|cuae2}!m10ux!mnc > AT&T Bell Labs (201)582-5911 MH 3B-416 > Murray Hill, NJ Oh no! Someone else just discovered this "bug". Now for another scintillating discussion for the next several weeks on whether a "void" expression actually returns a value or not ... Perhaps this ought to be included in the list of hints to new users on what not to post, along with any proofs of 1=0. -- Dave Horsfall (VK2KFU) ISD: +61 2 438-3544 FAX: 439-7036 UNIX Technical Support STD: (02) 438-3544 TLX: AA27411 NEC Information Systems Aust. ACS: dave@astra.necisa.oz (also CSNET) 3rd Floor, 99 Nicholson St ARPA: dave%astra.necisa.oz@seismo.css.gov St. Leonards NSW 2064 UUCP: {enea,hplabs,mcvax,prlb2,seismo, \ AUSTRALIA ubc-vision,ukc}!munnari!astra.necisa.oz!dave