下OS X GCC

Question

下面的代码C++编译在Windows上，但错误编译的Visual Studio 2012下就好了快递，Windows 8的

但在我的首选平台，Eclipse的朱诺，GCC 4.2 OS X 我收到以下错误：

../src/Test.cpp:20：错误： '的std :: istream的& TestNS ::运算符>>（的std :: istream的&，TestNS ::测试&）' 应该被宣布里面' TestNS'

#include <cstdio> 
#include <cstdlib> 
#include <iostream> 

using std::istream; 

namespace TestNS 
{ 
class Test 
{ 
    friend istream &operator>>(istream &in, Test &value); 

public: 
    Test(double real, double image); 

private: 
    double real; 
    double image; 
    void initialize(double real, double image); 

}; 
} 

#include <cstdio> 
#include <cstdlib> 
#include <iostream> 
#include "Header.h" 

using std::istream; 
using namespace TestNS; 

TestNS::Test::Test(double real = 0.0, double image = 0.0) : real(real), image(image) 
{ 

} 

void TestNS::Test::initialize(double real, double image) 
{ 
this->real = real; 
this->image = image; 
} 

istream& TestNS::operator>> (istream &in, TestNS::Test &value) 
{ 
value.real = 10.0; 
value.image = 10.0; 

return in; 

} 

int main() 
{ 

} 

任何帮助将是最有帮助的。 从事学校项目的作业。

Answer 1

看来GCC在给出错误方面是正确的。在您的示例中，operator>>的朋友声明确实指定operator>>将成为TestNS的成员，但实际上并未在此处声明。你仍然需要内部TestNS的operator>>声明之前，你可以在外面TestNS定义它：

namespace TestNS 
{ 
    class Test 
    { 
     friend istream &operator>>(istream &in, Test &value); 

    public: 
     Test(double real, double image); 

    private: 
     double real; 
     double image; 
     void initialize(double real, double image); 

    }; 

    istream &operator>>(istream &in,Test &value); // need this 
} 

现在，这是确定的：

istream& TestNS::operator>> (istream &in, TestNS::Test &value) 
{ 
    value.real = 10.0; 
    value.image = 10.0;   
    return in;  
} 

标准的相关部分是7.3.1.2 P2（用于C++ 03）：

Members of a named namespace can also be defined outside that namespace by explicit qualification of the name being defined, provided that the entity being defined was already declared in the namespace...

下一段指出（虽然有些间接），尽管类中的朋友声明确实使该函数成为名称空间的成员，但实际上并没有在那里声明它，因为函数的名称在名称空间内变得可见需要单独声明：

If a friend declaration in a non-local class first declares a class or function, the friend class or function is a member of the innermost enclosing namespace. The name of the friend function is not found by simple name lookup until a matching declaration is provided in that namespace scope (either before or after the class declaration granting friendship).