[英]C++ global extern “C” friend can't reach private member on namespaced class
Please consider the code: 请考虑以下代码:
#include <iostream>
using namespace std;
extern "C"
void foo( void );
namespace A
{
template< int No >
class Bar
{
private:
friend void ::foo( void );
static void private_func( int n );
};
template< int No >
void Bar< No >::private_func( int n )
{
cout << "A:Bar< " << No << ">::private_func( " << n << " )" << endl;
}
}
extern "C"
void foo( void )
{
A::Bar< 0 >::private_func( 1 );
}
int main( )
{
cout << " ---- " << endl;
foo( );
}
G++ gives: G ++提供:
> g++ -Wall -o extern_c extern_c.cpp
extern_c.cpp: In function ‘void foo()’:
extern_c.cpp:20:7: error: ‘static void A::Bar<No>::private_func(int) [with int No = 0]’ is private
extern_c.cpp:29:31: error: within this context
If I comment the namspace A
, it will compile and run correctly. 如果我评论
namspace A
,它将编译并正确运行。
What am I missing? 我想念什么?
I looked related topics, but could not find any that fits in my problem. 我查看了相关主题,但找不到适合我的问题的任何主题。
Thanks people. 谢谢大家
EDIT: 编辑:
I am now convinced that extern "C"
has nothing to do with the problem. 我现在确信,
extern "C"
与问题无关。 Please ignore it. 请忽略它。
It's a g++ bug. 这是一个g ++错误。 Exists in 4.4, fixed in 4.6.
存在于4.4中,已在4.6中修复。
UPD: It seems that it's triggered by a combination of template
and namespace
. UPD:它似乎是由
template
和namespace
的组合触发的。 extern "C"
is not relevant, as it may be commented out and the error remains. extern "C"
,因为它可能已被注释掉并且错误仍然存在。
I don't know the explanation, but if you put foo( ) into a namespace, it works. 我不知道其解释,但是如果将foo()放入命名空间中,它将起作用。
#include <iostream>
using namespace std;
namespace C
{
extern "C"
void foo( void );
}
namespace A
{
template< int No >
class Bar
{
private:
friend void C::foo( void );
static void private_func( int n );
};
template< int No >
void Bar< No >::private_func( int n )
{
cout << "A::Bar< " << No << ">::private_func( " << n << " )" << endl;
}
}
namespace C
{
extern "C"
void foo( void )
{
A::Bar< 0 >::private_func( 1 );
}
}
int main( )
{
cout << " ---- " << endl;
C::foo( );
}
And the result: 结果:
bbcaponi@bbcaponi friends]$ g++ -Wall namespace_friend.cpp -o namespace_friend
[bbcaponi@bbcaponi friends]$ ./namespace_friend
----
A::Bar< 0>::private_func( 1 )
You need to declare the friend as extern "C". 您需要将朋友声明为extern“ C”。 Your current friend declaration finds a friend foo in the global namespace that has C++ name mangling.
您当前的好友声明在全局名称空间中找到具有C ++名称修饰的好友foo。
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