C++模板：函数模板、类模板、模板与继承
C++模板：描述
C++提供一种模板的机制来减少代码重复。比如：对于同一样函数使用不同的数据类型，int,double,char等。C++模板属于“元编程”的范畴。
C++ 模板函数
1.支持不同数据类型的函数重载：
#include <iostream>
using namespace std;
int square (int x)
{
return x * x;
};
float square (float x)
{
return x * x;
};
double square (double x)
{
return x * x;
};
main()
{
int i, ii;
float x, xx;
double y, yy;
i = 2;
x = 2.2;
y = 2.2;
ii = square(i);
cout << i << ": " << ii << endl;
xx = square(x);
cout << x << ": " << xx << endl;
yy = square(y);
cout << y << ": " << yy << endl;
}
2.支持所有数据类型的函数模板
#include <iostream>
using namespace std;
template <class T>
inline T square(T x)
{
T result;
result = x * x;
return result;
};
main()
{
int i, ii;
float x, xx;
double y, yy;
i = 2;
x = 2.2;
y = 2.2;
ii = square<int>(i);
cout << i << ": " << ii << endl;
xx = square<float>(x);
cout << x << ": " << xx << endl;
// Explicit use of template
yy = square<double>(y);// 显式使用模板
cout << y << ": " << yy << endl;
yy = square(y);//隐含的方式使用模板
cout << y << ": " << yy << endl;
}
注明：模板的关键字可以用class或者typename.
- template<class T>
- template<typename T>
两者表达的意思是一样的，但是我更喜欢使用后者。
但是宏没有类型检查，函数模板有类型检查。
C++ 模板特例化
下面的例子字符串类型需要特殊处理，采用模板的特例化
#include <iostream>
using namespace std;
template <class T>
inline T square(T x)
{
T result;
result = x * x;
return result;
};
// 模板特殊化
template <>
string square<string>(string ss)
{
return (ss+ss);
};
main()
{
int i = 2, ii;
string ww("Aaa");
ii = square<int>(i);
cout << i << ": " << ii << endl;
cout << square<string>(ww) << endl;
}
注明：模板特例化用于当一个数据类型需要进行不同的处理和实现的情况。
C++ 模板无类型参数
#include <iostream>
using namespace std;
template <typename T, int count>
void loopIt(T x)
{
T val[count];
for(int ii=0; ii<count; ii++)
{
val[ii] = x++;
cout << val[ii] << endl;
}
};
main()
{
float xx = 2.1;
loopIt<float,3>(xx);
}
C++ 模板默认类型参数以及无类型参数
#include <iostream>
using namespace std;
template <typename T=float, int count=3>
T multIt(T x)
{
for(int ii=0; ii<count; ii++)
{
x = x * x;
}
return x;
};
main()
{
float xx = 2.1;
cout << xx << ": " << multIt<>(xx) << endl;;
}
注明：multIt<>没有指定参数类型，默认为float;
C++ 类模板
类模板定义：template <class T> class MyTemplateClass { ... };
类模板特例化：template <> class MyTemplateClass <specific-data-type> { ... };
File: Matrix2x2.hpp
#ifndef MATRIX_2X2_HPP__
#define MATRIX_2X2_HPP__
using namespace std;
/**
m(11) m(12)
m(21) m(22)
*/
template <class T>
class Matrix2x2
{
public:
Matrix2x2(T m11, T m12, T m21, T m22); //constructor
Matrix2x2(T m[2][2]);
Matrix2x2();
int Add(Matrix2x2 x)
int Multiply(Matrix2x2 x)
void Print();
T m[2][2];
};
template <class T>
Matrix2x2<T>::Matrix2x2(T _m11, T _m12, T _m21, T _m22)
{
m[0][0] = _m11;
m[0][1] = _m12;
m[1][0] = _m21;
m[1][1] = _m22;
}
template <class T>
Matrix2x2<T>::Matrix2x2(T _m)
{
m[0][0] = _m[0][0];
m[0][1] = _m[0][1];
m[1][0] = _m[1][0];
m[1][1] = _m[1][1];
}
template <class T>
Matrix2x2<T>::Matrix2x2()
{
m[0][0] = 0;
m[0][1] = 0;
m[1][0] = 0;
m[1][1] = 0;
}
template <class T>
Matrix2x2<T>::Add(Matrix2x2 _x)
{
Matrix2x2<T> sum;
sum.m[0][0] = m[0][0] + _x.m[0][0];
sum.m[0][1] = m[0][1] + _x.m[0][1];
sum.m[1][0] = m[1][0] + _x.m[1][0];
sum.m[1][1] = m[1][1] + _x.m[1][1];
return sum;
}
template <class T>
Matrix2x2<T>::Multiply(Matrix2x2 _x)
{
Matrix2x2<T> sum;
sum.m[0][0] = m[0][0] * _x.m[0][0] + m[0][1] * _x.m[1][0];
sum.m[0][1] = m[0][0] * _x.m[0][1] + m[0][1] * _x.m[1][1];
sum.m[1][0] = m[1][0] * _x.m[0][0] + m[1][1] * _x.m[1][0];
sum.m[1][1] = m[1][0] * _x.m[0][1] + m[1][1] * _x.m[1][1];
return sum;
}
template <class T>
Matrix2x2<T>::Print()
{
cout << "|" << m[0][0] << " " << m[0][1] << "|" << endl;
cout << "|" << m[1][0] << " " << m[1][1] << "|" << endl;
}
#endif
TestMatrix2x2.cpp
#include <iostream>
#include "Matrix2x2.hpp"
using namespace std;
int main(int argc, char* argv[])
{
Matrix2x2<int> X(1,2,3,4);
Matrix2x2<int> Y(5,6,7,8);
cout << "X:" << endl;
X.Print();
cout << "Y:" << endl;
Y.Print();
Matrix2x2<int> A = X.Add(Y);
cout << "A:" << endl;
A.Print();
Matrix2x2<int> B = X.Add(Y);
cout << "B:" << endl;
B.Print();
}
C++ 普通类和类模板的静态成员变量
普通类的静态成员函数：
#include <iostream>
using namespace std;
class XYZ
{
public:
void putPri();
static int ipub;
private:
static int ipri;
};
void XYZ::putPri()
{
cout << ipri++ << endl;
}
// 静态成员变量初始化:
int XYZ::ipub = 1;
int XYZ::ipri = 1;
main()
{
XYZ aaa;
XYZ bbb;
aaa.putPri();
cout << aaa.ipub << endl;
bbb.putPri();
}
类模板的静态成员：
#include <iostream>
using namespace std;
template <class T>
class XYZ
{
public:
void putPri();
static T ipub;
private:
static T ipri;
};
template <class T>
void XYZ<T>::putPri()
{
cout << ipri++ << endl;
}
// 静态成员初始化:
template <class T> T XYZ<T>::ipub = 1;
template <class T> T XYZ<T>::ipri = 1.2;
main()
{
XYZ<int> aaa;
XYZ<float> bbb;
aaa.putPri();
cout << aaa.ipub << endl;
bbb.putPri();
}
C++ 模板的模板参数
#include <iostream>
using namespace std;
template <template <typename T> typename U>
class Xyz
{
....
};
C++ 类模板和继承
Color.hpp (无模板的基类)
#ifndef COLOR_HPP__
#define COLOR_HPP__
#include <string>
enum eColor { none = 0, red, white, blue, yellow, green, black };
class Color
{
public:
Color(eColor color);
void setColor(eColor color);
eColor getColor() { return mColor; };
std::string getStrColor();
protected:
eColor mColor;
};
Color::Color(eColor _color)
{
mColor = _color;
}
void Color::setColor(eColor _color)
{
mColor = _color;
}
std::string Color::getStrColor()
{
switch(mColor)
{
case red:
return "red";
case white:
return "white";
case blue:
return "blue";
case yellow:
return "yellow";
case green:
return "green";
case black:
return "black";
case none:
default:
return "none";
}
}
#endif
File: Circle.hpp (模板基类)
#ifndef CIRCLE_HPP__
#define CIRCLE_HPP__
#include <math.h>
#include <string>
#include "Color.hpp"
template <typename T>
class Circle : public Color
{
public:
Circle(T centerX, T centerY, T radius, eColor color);
Circle(T centerX, T centerY, T radius);
Circle(T radius);
T area();
T circumference();
T getX();
T getY();
T getRadius();
protected:
T x;
T y;
T radius;
};
template <typename T>
Circle<T>::Circle(T _x, T _y, T _radius, eColor _color)
: Color(_color)
{
x = _x;
y = _y;
radius = _radius;
}
template <typename T>
Circle<T>::Circle(T _x, T _y, T _radius)
: Color(none)
{
x = _x;
y = _y;
radius = _radius;
}
template <typename T>
Circle<T>::Circle(T _radius)
: Color(none)
{
x = const_cast<T>(0);
y = const_cast<T>(0);
radius = _radius;
}
template <typename T>
T Circle<T>::area()
{
return M_PI * radius * radius;
}
template <typename T>
T Circle<T>::circumference()
{
return const_cast<T>(2) * M_PI * radius;
}
#endif
File: testCircle.cpp
#include <iostream>
#include "Circle.hpp"
using namespace std;
int main(int argc, char* argv[])
{
Circle<float> circleA(0.0, 0.0, 10.0, white);
cout << "Area: " << circleA.area() << endl;
cout << "Color: " << circleA.getStrColor() << endl;
}
一个模板类继承另外一个模板类：
File: Sphere.hpp (派生类)
#ifndef SPHERE_HPP__
#define SPHERE_HPP__
#include "Circle.hpp"
template <typename T>
class Sphere : public Circle<T>
{
public:
Sphere(T centerZ, T centerX, T centerY, T radius, eColor color);
Sphere(T radius);
Sphere();
T surfaceArea();
T volume();
T getZ();
private:
T z;
};
template <typename T>
Sphere<T>::Sphere(T _x, T _y, T _z, T _radius, eColor _color)
: Circle<T>::Circle (_x, _y, _radius, _color)
{
this->z = _z;
}
template <typename T>
Sphere<T>::Sphere(T _radius)
: Circle<T>::Circle (_radius)
{
this->x = const_cast<T>(0);
this->y = const_cast<T>(0);
this->z = const_cast<T>(0);
this->radius = _radius;
}
template <typename T>
Sphere<T>::Sphere()
{
this->x = const_cast<T>(0);
this->y = const_cast<T>(0);
this->z = const_cast<T>(0);
this->radius = const_cast<T>(1);
}
template <typename T>
T Sphere<T>::surfaceArea()
{
return const_cast<T>(4) * M_PI * this->radius * this->radius;
}
template <typename T>
T Sphere<T>::volume()
{
T three = 3;
T four = 4;
return four * M_PI * this->radius * this->radius * this->radius / three;
}
#endif
注明：用this来显示类的依赖
File: testSphere.cpp
#include <iostream>
#include "Sphere.hpp"
using namespace std;
int main(int argc, char* argv[])
{
Sphere<float> sphereA(0.0, 0.0, 0.0,10.0, blue);
cout << "Volume: " << sphereA.volume() << endl;
cout << "Color: " << sphereA.getStrColor() << endl;
}