C++ 之模板

15. 模板(Templates)

• Reuse source code
  • generic programming
  • use types as parameters in class or function definitions
• Template functions
• Template classes

15.1 Function Templates

• Perform similar operations on different types of data
• 示例：

// Swap function for two int arguments
void swap(int& x, int& y) {
    int temp = x;
    x = y;
    y = temp;
}

// swap function template
template <class T>
void swap(T& x, T& y) {
    T temp = x;
    x = y;
    y = temp;
}

// The template keyword introduces the template
// The class T specifies a parameterized type name
//    class means any built-in type or user-defined type
// Inside the template, use T as a type name

15.2 Class templates

• Classes parameterized by types
  • Abstract operations from the types being operated upon
  • Define potentially infinite set of classes
  • Another step towards reuse
• Typical use: container classes
  • stack <int>
  • list <Person&>
  • queue <Job>
• 示例：

template <class T>
class Vector {
public:
    Vector(int);
    ~Vector();
    Vector(const Vector&);
    Vector& operator=(const Vector&);
    T& operator[](int);
private:
    T* m_elements;
    int m_size;
};

// Vector 成员
template <class T>
Vector<T>::Vector(int size) : m_size(size) {
    m_elements = new T[m_size];
}

template <class T>
T& Vector<T>::operator[](int index) {
    if (index < m_size && index > 0) {
        return m_elements[index];
    } else {
        ...
    }
}

// 使用：
int main() {
    Vector<int> v1(100);
    Vector<Complex> v2(256);

    v1[20] = 10;
    v2[20] = v1[20];  // ok, if int => Complex defined
}

15.3 Templates and inheritance

• 示例：

// Templates can inherit from non-template classes
template <class A>
class Derived : public Base { ... }


// Templates can inherit from template classes
template <class A>
class Derived : public List<A> { ... }


// Non-template classes can inherit from templates
class SupervisorGroup : public List<Employee*> { ... }

参考资料：

• 翁凯 C++