命令空间中的函数是否只能通过使用命名空间作用域或using指令来访问？
我遇到一个问题，在命名空间内定义的某些函数可以访问该命名空间的OUTSIDE . 我相信应该有一个编译器错误，但我没有在我尝试过的三个不同的编译器中得到一个（VS.NET 2003，VS2010和GCC 4） .
这是代码：
namespace N{
typedef struct _some_type *some_type;
struct some_struct { int x; };
void A(void);
void B(int);
void C(some_type*);
void D(some_type);
void E(struct some_struct);
}
using N::some_type;
using N::some_struct;
void TestFunction()
{
some_type foo;
some_struct s;
N::A(); //should compile (and does on VS2003, VS2010, and GCC 4.1.2)
::A(); //shouldn't compile (and doesn't on VS2003, VS2010, and GCC 4.1.2)
A(); //shouldn't compile (and doesn't on VS2003, VS2010, and GCC 4.1.2)
N::B(0); //should compile (and does on VS2003, VS2010, and GCC 4.1.2)
::B(0); //shouldn't compile (and doesn't on VS2003, VS2010, and GCC 4.1.2)
B(0); //shouldn't compile (and doesn't on VS2003, VS2010, and GCC 4.1.2)
N::C(&foo); //should compile (and does on VS2003, VS2010, and GCC 4.1.2)
::C(&foo); //shouldn't compile (and doesn't on VS2003, VS2010, and GCC 4.1.2)
C(&foo); //shouldn't compile (but does on VS2003, VS2010, and GCC 4.1.2) -- problem!
N::D(foo); //should compile (and does on VS2003, VS2010, and GCC 4.1.2)
::D(foo); //shouldn't compile (and doesn't on VS2003, VS2010, and GCC 4.1.2)
D(foo); //shouldn't compile (but does on VS2003, VS2010, and GCC 4.1.2) -- problem!
N::E(s); //should compile (and does on VS2003, VS2010, and GCC 4.1.2)
::E(s); //shouldn't compile (and doesn't on VS2003, VS2010, and GCC 4.1.2)
E(s); //shouldn't compile (but does on VS2003, VS2010, and GCC 4.1.2) -- problem!
}
如果不使用N ::前缀，则不能访问任何函数，但C，D和E是出于某种未知原因 . 我最初认为这是一个编译器错误，但因为我在多个编译器中看到这个，它让我怀疑发生了什么 .
1 回答
我想你正在看到Koenig lookup的影响 . 在您的示例中，
foo和s是在命名空间N中定义的类型 . 您对例程C，D和E的调用使用这些类型的参数，因此搜索命名空间N以解析这些函数调用 .