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 函数重载的事实并不真正相关。 这里真正的问题是函数指针和成员函数指针之间的区别。 我将在不重载的情况下运行一些示例。 
 
 解决方案：删除static ，以便将它们定义为成员函数。 或者用' ns::ClassA::*ClassA_foo1替换ns::ClassA::*ClassA_foo1 *ClassA_foo1 。 我想你想要后者。 （但我实际上建议你使用typedef ，正如其他人已经建议的那样）。 
 
 考虑这两个： 
 
namespace ns {
struct ClassA
{
    static ClassA foo(long);
};
}
 
 和 
 
namespace ns {
struct ClassA
{
    ClassA foo(long);
};
}
 
 在前一种情况下，foo是static ，因此是一个典型的函数，可以存储在函数指针中： 
 
ns::ClassA (ClassA_foo1)(long) = &ns::ClassA::foo;
 
 如果你删除static ，那么它不再是一个函数，它是一个成员函数。 指向成员函数的指针与指向函数的指针不同，它们必须使用一个对象来执行，该对象将是调用该方法的对象。 
 
 函数指针的类型包括返回值的类型和参数的类型。 但是指向成员函数的指针类型还必须包含this对象的类型 - 您不希望能够在BankAccount类型的对象上从Circle运行方法。 
 
 声明指向函数的指针： 
 
 ReturnType (*variable_name) (PARAM1, PARAM2)
 
 声明指向成员函数的指针： 
 
 ReturnType (ThisObjectType::*variable_name) (PARAM1, PARAM2)
 
 最后一行是有趣的。 乍一看，您可能认为R (A::*v) (P1,P2)声明了一个正常的函数指针，并将结果变量v放入A范围。 但事实并非如此。 相反，它定义了一个指向成员的指针函数，该函数对类型A对象进行操作。 

The fact that the function is overloaded is not really relevant. The real issue here is the difference between a function-pointer and a member-function-pointer. I'll run through some examples without overloading.
 
Solution: Either remove the static, in order to define them as member-functions. Or else replace ns::ClassA::*ClassA_foo1 with *ClassA_foo1. I think you want the latter. (But I actually recommend you use typedef, as others have already suggested).
 
Consider these two:
 
namespace ns {
struct ClassA
{
    static ClassA foo(long);
};
}
 
and
 
namespace ns {
struct ClassA
{
    ClassA foo(long);
};
}
 
In the former case, foo is static and is therefore a typical function, and can be stored in a function-pointer:
 
ns::ClassA (ClassA_foo1)(long) = &ns::ClassA::foo;
 
If you remove the static, then it is not a function any more, it's a member function. And pointers-to-member-functions are different from pointers-to-functions, they must be executed with an object that will be the this object on which the method is called.
 
The type of a function pointer includes the type of the return value and the type of the parameters. But the type of a pointer-to-member-function must also include the type of the this object - you wouldn't expect to be able to run a method from a Circle on an object of type BankAccount.
 
Declaring a pointer-to-function:
 
 ReturnType (*variable_name) (PARAM1, PARAM2)
 
Declaring a pointer-to-member-function:
 
 ReturnType (ThisObjectType::*variable_name) (PARAM1, PARAM2)
 
This last line is the interesting one. At first glance, you might think that R (A::*v) (P1,P2) declares a normal function-pointer and places the resulting variable v into the A scope. But it does not. Instead it defines a pointer-to-member-function which operates on objects of type A.