http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56549
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: unassig...@gcc.gnu.org
ReportedBy: yurivk...@gmail.com
Created attachment 29594
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29594
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:
===
<BOM>#pragma once
struct Foo {};
===
stable.h:
===
#include "Foo.h"
===
main.cpp:
===
#include "stable.h"
int main() { Foo foo; }
===
Makefile:
===
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
===
Expected behavior:
===
$ make
g++ -x c++-header -c stable.h -o pragma-once.gch/c++
g++ -c -include pragma-once -o main.o main.cpp
===
Observed behavior:
===
$ 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 ‘struct Foo’
Foo.h:3:8: error: previous definition of ‘struct Foo’
make: *** [main.o] Error 1
===
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.
