brad@SSD.CSD.HARRIS.COM (Brad Appleton) (03/13/90)
Sorry to post this folks! I tried e-mail to both of her addresses but both bounced :-( In article <1990Mar9.045151.9601@ucselx.sdsu.edu> cynthia@ucselx.sdsu.edu (cynthia Anderson) writes: >hello > >i would like to be able to write a procedure that takes as >a parameter a procedure name and then using that name >calls the procedure. > >ie runAProcedure(myProcedure) > { > > > myProcedure > > >} > >Is this possible to do in C? Any help or advise is appreciated >tho please e-mail responses so the net won't be cluttered. > >thanks, > >cynthia anderson ><cynthia@cod.nosc.mil.uucp> >or ><cynthia@ucselx.sdsu.edu> > >Disclaimer: whenever it was and whenever it happened, i'm sure i >wasn't there and it couldn't have been me. NO! It is not possible to do in C! (Im pretty sure you cant do this in ANSI C either). What you can do is pass the address of a function to another function and call that function: int runAfunct( myfunct ) int (*myfunct)(); { (*myfunct)(); } int someFunct() { return 10; } main() { int i; i = runAfunct( someFunct ); printf( "%d\n", i ); exit( 0 ); } Hope this helps!!! +=-=-=-=-=-=-=-=-= "... and miles to go before I sleep." -=-=-=-=-=-=-=-=-=-+ | Brad Appleton | Harris Computer Systems Division | | | 2101 West Cypress Creek Road | | brad@ssd.csd.harris.com | Fort Lauderdale, FL 33309 USA | | ... {uunet | novavax}!hcx1!brad | MailStop 161 (305) 973-5007 | +=-=-=-=-=-=-=-=- DISCLAIMER: I said it, not my company! -=-=-=-=-=-=-=-=-=-+
brad@SSD.CSD.HARRIS.COM (Brad Appleton) (03/13/90)
OOPS -- I screwed up! the body of function "runAfunct" in my
previous post should have been "return (*myfunct)();"
not "(*myfunct)();" without the return !!!
My most sincere apologies.
incidentally, that brings up an interesting point! If I have a function
int foo() { int i; i = 10; }
without a specified return value, what will be returned when foo is called.
On one compiler I have used, it will return "10" because 10 was the last
"thing that was evaluated". I doubt that this is reliable however (is it?)
Should the compiler catch the "missing return" or is that left strictly
to lint?
advTHANXance
+=-=-=-=-=-=-=-=-= "... and miles to go before I sleep." -=-=-=-=-=-=-=-=-=-+
| Brad Appleton | Harris Computer Systems Division |
| | 2101 West Cypress Creek Road |
| brad@ssd.csd.harris.com | Fort Lauderdale, FL 33309 USA |
| ... {uunet | novavax}!hcx1!brad | MailStop 161 (305) 973-5007 |
+=-=-=-=-=-=-=-=- DISCLAIMER: I said it, not my company! -=-=-=-=-=-=-=-=-=-+CMH117@psuvm.psu.edu (Charles Hannum) (03/14/90)
In article <3243@hcx1.SSD.CSD.HARRIS.COM>, brad@SSD.CSD.HARRIS.COM (Brad Appleton) says: > >incidentally, that brings up an interesting point! If I have a function > > int foo() { int i; i = 10; } > >without a specified return value, what will be returned when foo is called. >On one compiler I have used, it will return "10" because 10 was the last >"thing that was evaluated". I doubt that this is reliable however (is it?) > >Should the compiler catch the "missing return" or is that left strictly >to lint? Old style C compilers that did not support the void type simply used int functions that didn't return a value. Thus, out of habit, some compilers *still* don't catch missing return values. There should at least be a warning you can turn on that will catch this, though you should be able to turn it off when working with old C programs. >advTHANXance Cute. Virtually, - Charles Martin Hannum II "Klein bottle for sale ... inquire within." (That's Charles to you!) "To life immortal!" cmh117@psuvm.{bitnet,psu.edu} "No noozzzz izzz netzzzsnoozzzzz..." c9h@psuecl.{bitnet,psu.edu} "Mem'ry, all alone in the moonlight ..."
karl@haddock.ima.isc.com (Karl Heuer) (03/14/90)
In article <3243@hcx1.SSD.CSD.HARRIS.COM> brad@SSD.CSD.HARRIS.COM (Brad Appleton) writes: >[The function int foo() { int i; i = 10; } will, on some compilers, >appear to have returned the value 10. Unreliable?] Very. What you're actually getting is whatever happened to be left lying around in the function-return-value register. >Should the compiler catch the "missing return" or is that left strictly >to lint? As far as the language definition goes, there is no distinction between cc and lint. This check is traditionally done only in lint because it generally requires cross-module analysis to know whether the value that isn't returned from foo() is actually being used anywhere. If it *isn't* being used, then the code is legal but sloppy (it should be declared "void"). This remains legal for for backward compatibility, and, unfortunately, a lot of code continues to depend on it. Karl W. Z. Heuer (karl@ima.ima.isc.com or harvard!ima!karl), The Walking Lint
gordon@sneaky.UUCP (Gordon Burditt) (03/15/90)
>>i would like to be able to write a procedure that takes as >>a parameter a procedure name and then using that name >>calls the procedure. >> >>ie runAProcedure(myProcedure) >> { >> myProcedure >>} >> >>Is this possible to do in C? Any help or advise is appreciated >>tho please e-mail responses so the net won't be cluttered. > >NO! It is not possible to do in C! (Im pretty sure you cant do this >in ANSI C either). Yes, it is. Some really old compilers did accept myfunct(), where myfunct is of type pointer-to-function-returning-something, as meaning the same as (*myfunct)(). Modern compilers tend to at least give warnings about it. From section 3.7.1 of the Jan 1988 ANSI C draft (sorry, that's the most recent one I have): QUOTE To pass one function to another, one might say int f(void) /* ... */ g(f); Note that f must be declared explicitly in the calling function, as its appearance in the expression g(f) was not followed by (. Then the definition of g might read g(int (*funcp)(void)) { /* ... */ (*funcp)() /* or funcp() ... */ } or, equivalently, g(int func(void)) { /* ... */ func() /* or (*func)() ... */ } END QUOTE. ANSI allows this, and even gives an example of it. Gordon L. Burditt sneaky.lonestar.org!gordon