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From: "yurivkhan at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug pch/56549] New: #pragma once ineffective with BOM in include file
Date: Wed, 06 Mar 2013 09:47:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D56549

             Bug #: 56549
           Summary: #pragma once ineffective with BOM in include file
    Classification: Unclassified
           Product: gcc
           Version: 4.6.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: pch
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: yurivkhan@gmail.com


Created attachment 29594
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=3D29594
Minimal example demonstrating the problem

When an include file starts with a UTF-8 byte order mark and is included in=
 a
precompiled header, it is not protected against repeated inclusion.

Environment:
 * Ubuntu 12.04 amd64
 * GCC 4.6.3 from Ubuntu repo

To reproduce:

$ unzip pragma-once-bom.zip
$ make

The contents of the archive are listed below for convenience of discussion.

Foo.h:
=3D=3D=3D
<BOM>#pragma once

struct Foo {};
=3D=3D=3D

stable.h:
=3D=3D=3D
#include "Foo.h"
=3D=3D=3D

main.cpp:
=3D=3D=3D
#include "stable.h"

int main() { Foo foo; }
=3D=3D=3D

Makefile:
=3D=3D=3D
all: main.o

pragma-once.gch/c++: stable.h Foo.h
    @test -d pragma-once.gch || mkdir pragma-once.gch
    g++ -x c++-header -c stable.h -o pragma-once.gch/c++

main.o: main.cpp stable.h Foo.h pragma-once.gch/c++
    g++ -c -include pragma-once -o main.o main.cpp

clean:
    @rm -rf pragma-once.gch main.o
=3D=3D=3D

Expected behavior:

=3D=3D=3D
$ make
g++ -x c++-header -c stable.h -o pragma-once.gch/c++
g++ -c -include pragma-once -o main.o main.cpp
=3D=3D=3D

Observed behavior:

=3D=3D=3D
$ make
g++ -x c++-header -c stable.h -o pragma-once.gch/c++
g++ -c -include pragma-once -o main.o main.cpp
In file included from stable.h:1:0,
                 from main.cpp:1:
Foo.h:3:8: error: redefinition of =E2=80=98struct Foo=E2=80=99
Foo.h:3:8: error: previous definition of =E2=80=98struct Foo=E2=80=99
make: *** [main.o] Error 1
=3D=3D=3D

Workarounds/observations:

* If the header file does not contain a BOM, the problem does not occur.
* With include guards instead of #pragma once, the problem does not occur.
* In a real project, changing an #include <FooLib/Foo.h> to #include
<FooLib/./Foo.h> in the precompiled header stable.h, or changing an #include
<FooLib/Foo.h> to #include "Foo.h" in a different header included by stable=
.h,
also fixes the immediate problem.