c++/3390: Can't pass a reference to temporary objects

c++/3390: Can't pass a reference to temporary objects

[prewett]

>Number:         3390
>Category:       c++
>Synopsis:       Can't pass a reference to temporary objects
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          rejects-legal
>Submitter-Id:   net
>Arrival-Date:   Sat Jun 23 14:06:01 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Geoff Prewett
>Release:        gcc-3.0
>Organization:
>Environment:
Reading specs from /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0/specs
Configured with: ../gcc-3.0/configure 
Thread model: single
gcc version 3.0
GNU CPP version 3.0 (cpplib) (i386 Linux/ELF)
GNU C++ version 3.0 (i686-pc-linux-gnu)
        compiled by GNU C version 2.96 20000731 (Red Hat Linux 7.1 2.96-81).
>Description:
Gcc-3.0 does not appear to allow references to temporary
objects.  This makes it rather inconvenient to do:

class Vector { ... };
void Munge(Vector& arg1, Vector& arg2, Vector& arg3);
{
   Vector x, y;
   Munge(x + y, x - y, x + x);
}

This is very similar to bug report 3230.
>How-To-Repeat:
test.cpp:
---------------------------------------------------------------------
int invert(int& x)
{
        return(-x);
}

int problem()
{
        int x = -5, y = 5, z;

        invert(x + y);          // error

        z = x + y;              // works
        invert(z);
}
---------------------------------------------------------------------
> gcc -v -save-temp test.cpp
Reading specs from /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0/specs
gcc: unrecognized option `-save-temp'
Configured with: ../gcc-3.0/configure 
Thread model: single
gcc version 3.0
 /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0/cc1plus -v -D__GNUC__=3 -D__GNUC_MINOR__=0 -D__GNUC_PATCHLEVEL__=0 -D__ELF__ -Dunix -Dlinux -D__ELF__ -D__unix__ -D__linux__ -D__unix -D__linux -Asystem=posix -D__NO_INLINE__ -D__STDC_HOSTED__=1 -D_GNU_SOURCE -Acpu=i386 -Amachine=i386 -Di386 -D__i386 -D__i386__ -D__tune_i686__ -D__tune_pentiumpro__ test.cpp -D__GNUG__=3 -D__GXX_DEPRECATED -D__EXCEPTIONS -D__GXX_ABI_VERSION=100 -quiet -dumpbase test.cpp -version -o /tmp/ccxreRzz.s
GNU CPP version 3.0 (cpplib) (i386 Linux/ELF)
GNU C++ version 3.0 (i686-pc-linux-gnu)
        compiled by GNU C version 2.96 20000731 (Red Hat Linux 7.1 2.96-81).
ignoring nonexistent directory "/usr/local/i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include/g++-v3
 /usr/local/include/g++-v3/i686-pc-linux-gnu
 /usr/local/include/g++-v3/backward
 /usr/local/include
 /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0/include
 /usr/include
End of search list.
test.cpp: In function `int problem()':
test.cpp:10: could not convert `(x + y)' to `int&'
test.cpp:2: in passing argument 1 of `int invert(int&)'
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:

Re: c++/3390: Can't pass a reference to temporary objects

[aoliva]

Synopsis: Can't pass a reference to temporary objects

State-Changed-From-To: open->closed
State-Changed-By: aoliva
State-Changed-When: Tue Jun 26 13:32:58 2001
State-Changed-Why:
    The C++ Standard allows temporaries to be bound to const references, but not to non-const references.  GCC just follows the Standard.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view&pr=3390&database=gcc