如何设置表示接口的类?这只是一个抽象基类吗?
当前回答
如果您只需要接口的静态绑定(没有虚拟的,没有接口类型本身的实例,接口仅作为指南):
#include <iostream>
#include <string>
// Static binding interface
// Notice: instantiation of this interface should be usefuless and forbidden.
class IBase {
protected:
IBase() = default;
~IBase() = default;
public:
// Methods that must be implemented by the derived class
void behaviorA();
void behaviorB();
void behaviorC() {
std::cout << "This is an interface default implementation of bC().\n";
};
};
class CCom : public IBase {
std::string name_;
public:
void behaviorA() { std::cout << "CCom bA called.\n"; };
};
class CDept : public IBase {
int ele_;
public:
void behaviorB() { std::cout << "CDept bB called.\n"; };
void behaviorC() {
// Overwrite the interface default implementation
std::cout << "CDept bC called.\n";
IBase::behaviorC();
};
};
int main(void) {
// Forbid the instantiation of the interface type itself.
// GCC error: ‘constexpr IBase::IBase()’ is protected within this context
// IBase o;
CCom acom;
// If you want to use these interface methods, you need to implement them in
// your derived class. This is controled by the interface definition.
acom.behaviorA();
// ld: undefined reference to `IBase::behaviorB()'
// acom.behaviorB();
acom.behaviorC();
CDept adept;
// adept.behaviorA();
adept.behaviorB();
adept.behaviorC();
// adept.IBase::behaviorC();
}
其他回答
为了扩展bradtgmurray的答案,您可能希望通过添加虚拟析构函数来对接口的纯虚拟方法列表进行一个例外。这允许您将指针所有权传递给另一方,而不暴露具体的派生类。析构函数不必做任何事情,因为接口没有任何具体的成员。将函数定义为虚拟函数和内联函数可能看起来很矛盾,但相信我,事实并非如此。
class IDemo
{
public:
virtual ~IDemo() {}
virtual void OverrideMe() = 0;
};
class Parent
{
public:
virtual ~Parent();
};
class Child : public Parent, public IDemo
{
public:
virtual void OverrideMe()
{
//do stuff
}
};
您不必为虚拟析构函数包含一个主体——事实证明,某些编译器在优化空析构函数时遇到了问题,最好使用默认值。
class Shape
{
public:
// pure virtual function providing interface framework.
virtual int getArea() = 0;
void setWidth(int w)
{
width = w;
}
void setHeight(int h)
{
height = h;
}
protected:
int width;
int height;
};
class Rectangle: public Shape
{
public:
int getArea()
{
return (width * height);
}
};
class Triangle: public Shape
{
public:
int getArea()
{
return (width * height)/2;
}
};
int main(void)
{
Rectangle Rect;
Triangle Tri;
Rect.setWidth(5);
Rect.setHeight(7);
cout << "Rectangle area: " << Rect.getArea() << endl;
Tri.setWidth(5);
Tri.setHeight(7);
cout << "Triangle area: " << Tri.getArea() << endl;
return 0;
}
结果:矩形面积:35三角形面积:17
我们已经看到了抽象类是如何根据getArea()定义接口的,另外两个类实现了相同的函数,但使用了不同的算法来计算特定于形状的面积。
我还是C++开发的新手。我从Visual Studio(VS)开始。
然而,似乎没有人提到VS(.NET)中的__interface。我不太确定这是否是声明接口的好方法。但它似乎提供了额外的强制执行(文件中提到)。这样就不必显式指定虚拟TYPE Method()=0;,因为它将被自动转换。
__interface IMyInterface {
HRESULT CommitX();
HRESULT get_X(BSTR* pbstrName);
};
然而,我不使用它,因为我担心跨平台编译兼容性,因为它只在.NET下可用。
如果有人对此感兴趣,请分享。:-)
谢谢
如果您使用的是Microsoft的C++编译器,则可以执行以下操作:
struct __declspec(novtable) IFoo
{
virtual void Bar() = 0;
};
class Child : public IFoo
{
public:
virtual void Bar() override { /* Do Something */ }
}
我喜欢这种方法,因为它会产生更小的接口代码,生成的代码大小也会明显更小。novtable的使用删除了该类中对vtable指针的所有引用,因此您永远不能直接实例化它。请参阅此处的文档-novtable。
如果您只需要接口的静态绑定(没有虚拟的,没有接口类型本身的实例,接口仅作为指南):
#include <iostream>
#include <string>
// Static binding interface
// Notice: instantiation of this interface should be usefuless and forbidden.
class IBase {
protected:
IBase() = default;
~IBase() = default;
public:
// Methods that must be implemented by the derived class
void behaviorA();
void behaviorB();
void behaviorC() {
std::cout << "This is an interface default implementation of bC().\n";
};
};
class CCom : public IBase {
std::string name_;
public:
void behaviorA() { std::cout << "CCom bA called.\n"; };
};
class CDept : public IBase {
int ele_;
public:
void behaviorB() { std::cout << "CDept bB called.\n"; };
void behaviorC() {
// Overwrite the interface default implementation
std::cout << "CDept bC called.\n";
IBase::behaviorC();
};
};
int main(void) {
// Forbid the instantiation of the interface type itself.
// GCC error: ‘constexpr IBase::IBase()’ is protected within this context
// IBase o;
CCom acom;
// If you want to use these interface methods, you need to implement them in
// your derived class. This is controled by the interface definition.
acom.behaviorA();
// ld: undefined reference to `IBase::behaviorB()'
// acom.behaviorB();
acom.behaviorC();
CDept adept;
// adept.behaviorA();
adept.behaviorB();
adept.behaviorC();
// adept.IBase::behaviorC();
}