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* Re: c++/5296: Pointers to functions and template functions behave differentl
@ 2002-04-29 14:16 Noel Yap
0 siblings, 0 replies; 3+ messages in thread
From: Noel Yap @ 2002-04-29 14:16 UTC (permalink / raw)
To: nobody; +Cc: gcc-prs
The following reply was made to PR c++/5296; it has been noted by GNATS.
From: Noel Yap <nyap@OLF.COM>
To: "'wolfgang.bangerth@iwr.uni-heidelberg.de'"
<wolfgang.bangerth@iwr.uni-heidelberg.de>,
"'gcc-gnats@gcc.gnu.org'"
<gcc-gnats@gcc.gnu.org>,
"'gcc-prs@gcc.gnu.org'" <gcc-prs@gcc.gnu.org>,
"'gcc-bugs@gcc.gnu.org'" <gcc-bugs@gcc.gnu.org>,
"'nobody@gcc.gnu.org'"
<nobody@gcc.gnu.org>
Cc:
Subject: Re: c++/5296: Pointers to functions and template functions behave
differentl
Date: Mon, 29 Apr 2002 17:14:30 -0400
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<TITLE>Re: c++/5296: Pointers to functions and template functions =
behave differentl</TITLE>
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<P><FONT SIZE=3D2 FACE=3D"Arial"><A =
HREF=3D"http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=3Dview%20audit-trail&=
database=3Dgcc&pr=3D5296" =
TARGET=3D"_blank">http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=3Dview%20au=
dit-trail&database=3Dgcc&pr=3D5296</A></FONT>
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<P><FONT SIZE=3D2 FACE=3D"Arial">I've found one or two (depending on if =
you count them to be the same or not) workarounds for this:</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">1. original snippet:</FONT>
<BR><FONT FACE=3D"Courier New">int main () {<BR>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 print_type (&pp1);<BR>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 print_type (&pp2<int>);<BR>
=A0 =A0 =A0 =A0 =A0 =A0 =
=A0};</FONT><FONT FACE=3D"Arial"> </FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">workaround (note that reinterpret_cast =
will NOT work here):</FONT>
<BR><FONT FACE=3D"Courier New">int main () {<BR>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 print_type (&pp1);<BR>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 print_type ((void (*)(int)) &pp2<int>);<BR>
=A0 =A0 =A0 =A0 =A0 =A0 =
=A0};</FONT><FONT FACE=3D"Arial"> </FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">2. original snippet:</FONT>
<BR><FONT FACE=3D"Courier New">int main () {<BR>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 print_type (&pp1);<BR>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 print_type (&pp2<int>);<BR>
=A0 =A0 =A0 =A0 =A0 =A0 =
=A0};</FONT><FONT FACE=3D"Arial"> </FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">workaround:</FONT>
<BR><FONT FACE=3D"Courier New">int main () {</FONT>
<BR> =
=
<FONT FACE=3D"Courier =
New">void (*pp2p)(int) =3D &pp2<int>;</FONT>
<BR>
<BR><FONT FACE=3D"Courier New">=A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 print_type (&pp1);<BR>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 print_type (pp2p);<BR>
=A0 =A0 =A0 =A0 =A0 =A0 =
=A0};</FONT><FONT FACE=3D"Arial"> </FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">I think the fact that reinterpret_cast =
has problems points to the fact that the compiler really doesn't know =
what the type is (and hence, the {unknown_type} in the error =
message).</FONT></P>
<P><FONT SIZE=3D2 FACE=3D"Arial">Noel Yap</FONT>
</P>
<BR>
<P><B><FONT SIZE=3D2 FACE=3D"Arial">=A9 2002 OpenLink Financial =
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: c++/5296: Pointers to functions and template functions behave differentl
@ 2002-04-26 5:32 nathan
0 siblings, 0 replies; 3+ messages in thread
From: nathan @ 2002-04-26 5:32 UTC (permalink / raw)
To: gcc-bugs, gcc-prs, nobody, wolfgang.bangerth
Synopsis: Pointers to functions and template functions behave differentl
State-Changed-From-To: open->analyzed
State-Changed-By: nathan
State-Changed-When: Fri Apr 26 05:30:14 2002
State-Changed-Why:
confirmed
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5296
^ permalink raw reply [flat|nested] 3+ messages in thread
* c++/5296: Pointers to functions and template functions behave differentl
@ 2002-01-07 2:16 wolfgang.bangerth
0 siblings, 0 replies; 3+ messages in thread
From: wolfgang.bangerth @ 2002-01-07 2:16 UTC (permalink / raw)
To: gcc-gnats
>Number: 5296
>Category: c++
>Synopsis: Pointers to functions and template functions behave differentl
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: rejects-legal
>Submitter-Id: net
>Arrival-Date: Mon Jan 07 02:16:01 PST 2002
>Closed-Date:
>Last-Modified:
>Originator: Wolfgang Bangerth
>Release: unknown-1.0
>Organization:
>Environment:
2.95.2 and 3.0.1 and SS20011107
checked on Sun and Linux
>Description:
Pointers to regular functions and to template functions behave
differently. A simple example to show this is this:
#include <iostream>
#include <typeinfo>
template <typename T> void print_type (const T &) {
std::cout << typeid(T).name() << std::endl;
};
/* no template */ void pp1 (int) {};
template <typename X> void pp2 (X) {};
int main () {
print_type (&pp1);
print_type (&pp2<int>);
};
We try to print the data types (mangled) of a pointer to a function
and a pointer to a template function. With gcc2.95.2, this example is
compilable and yields as output:
examples/step-1> c++ b.cc
examples/step-1> ./a.out
---> PFi_v
---> Fi_v
examples/step-1> c++ -v
Reading specs from /usr/lib/gcc-lib/i486-suse-linux/2.95.2/specs
gcc version 2.95.2 19991024 (release)
The two lines of output should be identical, but are not. With
gcc3.0.1 and SS20011107, the example is not compilable:
examples/step-1> ~/bin/gcc-3.0.1/bin/c++ b.cc
b.cc: In function `int main()':
b.cc:13: no matching function for call to `print_type(<unknown type>)'
examples/step-1> ~/bin/gcc-3.0.1/bin/c++ -v
Reading specs from /home/wolf/bin/gcc-3.0.1/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/specs
Configured with: ../gcc-3.0.1/configure --prefix=/home/wolf/bin/gcc-3.0.1
Thread model: single
gcc version 3.0.1
Note that for both gcc versions, the problem disappears if we let
print_type take an argument of type `T' rather than `const T &'
(very strange).
The effect shown above results in the non-compilability of the
following example program:
template <typename T> struct Capsule { T t; };
template <typename T> void encapsulate (const T &) { Capsule<T> c; };
/* no template */ void pp1 (int);
template <typename X> void pp2 (X);
void foo() {
encapsulate (&pp1); // ok
encapsulate (&pp2<int>); // fails!?!
};
With gcc2.95.2:
examples/step-1> c++ -c a.cc
a.cc: In instantiation of `Capsule<void ()(int)>':
a.cc:3: instantiated from `encapsulate<void ()(int)>(void (&)(int))'
a.cc:10: instantiated from here
a.cc:1: field `Capsule<void ()(int)>::t' invalidly declared function type
^^^^^^^^^^^^
Note that the template type of the Capsule class for the second
(template function) is a reference to a function rather than a
pointer. With gcc3.0.1 and SS20011107, the error message is again
rather unhelpful:
examples/step-1> ~/bin/gcc-3.0.1/bin/c++ -c a.cc
a.cc: In function `void foo()':
a.cc:10: no matching function for call to `encapsulate(<unknown type>)'
>How-To-Repeat:
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted:
^ permalink raw reply [flat|nested] 3+ messages in thread
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2002-04-29 14:16 c++/5296: Pointers to functions and template functions behave differentl Noel Yap
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2002-04-26 5:32 nathan
2002-01-07 2:16 wolfgang.bangerth
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