// Illustrates some bugs related to __attribute__((warn_unused_result)).
struct Vector {
float x, y, z;
inline Vector() {}
inline Vector(float _x,float _y,float _z) : x(_x), y(_y), z(_z) {}
// BUG: Toggling the presence of a copy constructor (doesn't matter
which
// of the ones below you use) will affect the generation of the
warnings.
inline Vector(const Vector &a) { x = a.x; y = a.y; z = a.z; }
// inline Vector(const Vector &a) : x(a.x), y(a.y), z(a.z) {}
inline Vector operator-(const Vector &a) const
__attribute__((warn_unused_result)) {
return Vector(x - a.x, y - a.y, z - a.z );
}
};
struct Box {
Vector min, max;
// BUG: generates spurrious warning about not using result from
operator-.
// If you remove the copy constructor, the warning goes away
inline Vector size() const { return max - min; }
};
void foo() {
Vector a, b;
// BUG: this *should* generate a warning, but you will only get a
warning
// if you have the copy constructor. If you remove the copy
constructor,
// the warning goes away
a-b;
}
//
// Output with copy constructor defined:
//
// $ /c/usr/local/cell/host-win32/ppu/ppu-lv2/bin/gcc -v -save-temps -c -Wall
warn_unused_result_bug_2.cpp
// Using built-in specs.
// Target: ppu-lv2
// Configured with: /export/fukuoka/ps3-svn/toolchain/trunk/gcc/configure
--target=ppu-lv2 --host=i386-pc-mingw32msvc --build=i686-pc-linux-gnu
--prefix=/usr/local/cell/host-win32/ppu
--with-sysroot=/usr/local/cell/target/ppu --with-headers=yes --disable-threads
--disable-shared --disable-hosted-libstdcxx
// Thread model: single
// gcc version 4.0.2 (CELL 4.1.19, $Rev: 1341 $)
// /usr/local/cell/host-win32/ppu/libexec/gcc/ppu-lv2/4.0.2/cc1plus.exe -E
-quiet -v -iprefix
c:\usr\local\cell\host-win32\ppu\ppu-lv2\bin\../lib/gcc/ppu-lv2/4.0.2/
-D__PPU__ -D__CELLOS_LV2__ warn_unused_result_bug_2.cpp -mabi=altivec -maltivec
-mstrict-align -fstrict-aligned -mvrsave=no -mtraceback=none -Wall
-fpch-preprocess -fno-threadsafe-statics -o warn_unused_result_bug_2.ii
// ignoring nonexistent directory
"c:/usr/local/cell/host-win32/ppu/ppu-lv2/bin/../lib/gcc/ppu-lv2/4.0.2/include"
// #include "..." search starts here:
// #include <...> search starts here:
// /usr/local/cell/host-win32/ppu/lib/gcc/ppu-lv2/4.0.2/include
// /usr/local/cell/target/ppu/include
// /usr/local/cell/target/ppu/include/sys
// /usr/local/cell/target/ppu/../common/include
// End of search list.
// /usr/local/cell/host-win32/ppu/libexec/gcc/ppu-lv2/4.0.2/cc1plus.exe
-fpreprocessed warn_unused_result_bug_2.ii -mabi=altivec -maltivec
-mstrict-align -fstrict-aligned -mvrsave=no -mtraceback=none -quiet -dumpbase
warn_unused_result_bug_2.cpp -auxbase warn_unused_result_bug_2 -Wall -version
-fno-threadsafe-statics -o warn_unused_result_bug_2.s
// GNU C++ version 4.0.2 (CELL 4.1.19, $Rev: 1341 $) (ppu-lv2)
// compiled by GNU C version 4.0.2 (CELL 4.1.19, $Rev: 1341 $).
// GGC heuristics: --param ggc-min-expand=99 --param ggc-min-heapsize=130941
// warn_unused_result_bug_2.cpp: In member function 'Vector Box::size()
const':
// warn_unused_result_bug_2.cpp:23: warning: ignoring return value of 'Vector
Vector::operator-(const Vector&) const', declared with attribute
warn_unused_result
// warn_unused_result_bug_2.cpp: In function 'void foo()':
// warn_unused_result_bug_2.cpp:32: warning: ignoring return value of 'Vector
Vector::operator-(const Vector&) const', declared with attribute
warn_unused_result
//
// If you comment out the copy constructor, the warnings do not appear.
// Note that I produced this with the Playstation (CELL) version of GCC under
// MinGW/MSys, but I don't think this is a platform specific issues.
//
// gccc --version produces this:
// gcc.exe (GCC) 4.0.2 (CELL 4.1.19, $Rev: 1341 $)
// Copyright (C) 2005 Free Software Foundation, Inc.
// This is free software; see the source for copying conditions. There is NO
// warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
//
// This might be a dup of either of these issues:
// http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27370
// http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27371
//
// Cheers,
// fletcherdunn --at-- yahoo.com
//
--
Summary: Spurrious/missing warn_unused_result warnings affected
by presence/absense of copy constructor
Product: gcc
Version: 4.0.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: fletcherdunn at yahoo dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31063
