非成员函数可以声明多次，而成员函数只能声明一次？

发布于 2024-12-06 06:48:30 字数 406 浏览 5 评论 0原文

非成员函数可以声明多次，而成员函数只能声明一次？这是对的吗？我的例子似乎说是的。

但为什么？

class Base{
public:
    int foo(int i);
    //int foo(int i=10); //error C2535: 'void Base::foo(int)' : member function already defined or declared
};

//but it seems ok to declare it multiple times
int foo(int i);
int foo(int i=10);

int foo(int i)
{
    return i;
}

int main (void)
{
    int i = foo();//i is 10 
}

原文

Non mumber function can be delcared multiple times while member function can only be declared once? Is this right ? My example seems saying yes.

But Why ?

class Base{
public:
    int foo(int i);
    //int foo(int i=10); //error C2535: 'void Base::foo(int)' : member function already defined or declared
};

//but it seems ok to declare it multiple times
int foo(int i);
int foo(int i=10);

int foo(int i)
{
    return i;
}

int main (void)
{
    int i = foo();//i is 10 
}

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猫九 2024-12-13 06:48:30

根据标准 (2003)，§8.3.6/4 说，

对于非模板函数，默认
参数可以稍后添加
同一函数中的函数声明
范围。

标准本身的示例：

void f(int, int);
void f(int, int = 7);

第二个声明添加了默认值！

另请参阅§8.3.6/6。

还有一个有趣的（并且有些相关）主题：

Default argument in the middle参数列表？

和§9.3/2，

除了出现在类定义之外的成员函数定义，以及出现在类定义之外的类模板和成员函数模板 (14.7) 的成员函数的显式特化之外，成员函数
不得重新声明。

希望有所帮助。

From the Standard (2003), §8.3.6/4 says,

For non-template functions, default
arguments can be added in later
declarations of a function in the same
scope.

Example from the Standard itself:

void f(int, int);
void f(int, int = 7);

The second declaration adds default value!

Also see §8.3.6/6.

And an interesting (and somewhat related) topic:

Default argument in the middle of parameter list?

And §9.3/2,

Except for member function definitions that appear outside of a class definition, and except for explicit specializations of member functions of class templates and member function templates (14.7) appearing outside of the class definition, a member function
shall not be redeclared.

Hope that helps.

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无戏配角 2024-12-13 06:48:30

使用这个简化版本您会得到相同的结果：

int foo() ;
int foo() ; // OK -- extern functions may be declared more than once
class C {
  int foo() ;
  int foo() ; // Error -- member function may not be declared more than once
} ;

也许原因是历史性的 - 许多 C 代码使用了 extern 函数的重新声明，因此必须允许它们。

You get the same result with this simplified version:

int foo() ;
int foo() ; // OK -- extern functions may be declared more than once
class C {
  int foo() ;
  int foo() ; // Error -- member function may not be declared more than once
} ;

Perhaps the reason is historical -- lots of C code used redeclaration of extern functions, so they had to be allowed.

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