G++ doesn't handle pointers to functions

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3 total messages Started by Jonathan D. Becher Tue, 11 Oct 1988 21:45

#1495

Author: Jonathan D. Becher
Date: Tue, 11 Oct 1988 21:45

37 lines
1218 bytes

The following program compiles with gcc but not with g++.
It seems as if g++ doesn't understand formal parameters that
are pointers to functions.
If anyone can think of a way around this bug (or explain to me 
why it isn't one), please let me know.
I can't live without pointers to functions :->

Program:

#include <stdio.h>
doSomething()
{
    printf("I did\n");
}

doThis(int (*f)())
{
    f();
}

main()
{
    doThis(doSomething);
}

Compilation:

g++ version 1.25.0
/usr/local/lib/gcc-cpp+ -v -undef -D__GNU__ -D__GNUG__ -Dvax -Dunix t.cc /tmp/cc011037.cpp
/usr/local/lib/gcc-c++ /tmp/cc011037.cpp -quiet -dumpbase t.cc -noreg -version -o /tmp/cc011037.s
GNU C++ version 1.25.0 (vax) compiled by GNU C version 1.25.
t.cc:9: undeclared variable `f' (first use here)


=====
Jon Becher
becher@cs.duke.edu          -OR-           argosy!becher@decwrl.dec.com

Re: G++ doesn't handle pointers to functions

#1494

Author: Jonathan D. Becher
Date: Tue, 11 Oct 1988 22:18

24 lines
949 bytes

In article <68@armada.UUCP>, I write:
   > It seems as if g++ doesn't understand formal parameters that
   > are pointers to functions.

In my previous posting, you can get around this error by using a typedef.
For some reason, this:
   > doThis(int (*f)())
   > {
   >     f();
   > }
doesn't work but this does:
   typedef int (*ptrFunc)();
   doThis(ptrFunc f)
   {
       f();
   }

In any event, it's still a bug.
=====
Jon Becher
becher@cs.duke.edu          -OR-           argosy!becher@decwrl.dec.com

"I go to parties, some times until four.
 It's hard to leave when you can't find the door."

G++ doesn't handle pointers to functions

#1496

Author: Michael Tiemann
Date: Wed, 12 Oct 1988 00:25

32 lines
1772 bytes

   Date: 11 Oct 88 21:45:49 GMT
   From: armada!becher@decwrl.dec.com  (Jonathan D. Becher)
   Organization: I have no organization (look at my desk)
   Sender: bug-g++-request@prep.ai.mit.edu

   The following program compiles with gcc but not with g++.
   It seems as if g++ doesn't understand formal parameters that
   are pointers to functions.
   If anyone can think of a way around this bug (or explain to me 
   why it isn't one), please let me know.
   I can't live without pointers to functions :->

From your previous posting, it is clear that you already know that
using a typedef solves this problem.  By using a typedef, you save
compilation time (less declarator structure to grok).  If, however,
you are somehow alergic to using typedefs, one thing you can do is this:

  doThis(auto int (*f)())
  {
      f();
  }

This will (or should) then compile.  This is a bug in the C++
language.  I wish that the designers of C++ knew enough about LALR
parsing to have made their language LALR-parsable; unfortunately, they
did not.  I consider the AT&T solution (which also doesn't always work
for pointers to functions in parameter positions) of using heuristics
to help try to guide the parser unacceptable, and certainly something
which I would want to distribute, freely or otherwise.

Michael

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