14.3 - Template classes

来源：互联网发布：python账号注册登录编辑：程序博客网时间：2024/05/19 21:42

Templates and container classes

首先我们看下面的类

class IntArray{private:    int m_nLength;    int *m_pnData; public:    IntArray()    {        m_nLength = 0;        m_pnData = 0;    }     IntArray(int nLength)    {        m_pnData = new int[nLength];        m_nLength = nLength;    }     ~IntArray()    {        delete[] m_pnData;    }     void Erase()    {        delete[] m_pnData;        // We need to make sure we set m_pnData to 0 here, otherwise it will        // be left pointing at deallocated memory!        m_pnData = 0;        m_nLength = 0;    }     int& operator[](int nIndex)    {        assert(nIndex >= 0 && nIndex < m_nLength);        return m_pnData[nIndex];    }     int GetLength() { return m_nLength; }};

使用这个类，我们可以方便的创建整数数组，但是如果我们想要创建double数组，传统的做法需要创建一个全新的类。使用template class则是一个简单高效的新方法。

template <typename T>class Array{private:    int m_nLength;    T *m_ptData; public:    Array()    {        m_nLength = 0;        m_ptData = 0;    }     Array(int nLength)    {        m_ptData= new T[nLength];        m_nLength = nLength;    }     ~Array()    {        delete[] m_ptData;    }     void Erase()    {        delete[] m_ptData;        // We need to make sure we set m_pnData to 0 here, otherwise it will        // be left pointing at deallocated memory!        m_ptData= 0;        m_nLength = 0;    }     T& operator[](int nIndex)    {        assert(nIndex >= 0 && nIndex < m_nLength);        return m_ptData[nIndex];    }     // The length of the array is always an integer    // It does not depend on the data type of the array    int GetLength(); // templated GetLength() function defined below}; template <typename T>int Array<T>::GetLength() { return m_nLength; }

值得注意的是我们在类的外面定义了GetLength()成员函数。这就需要这个函数有自己的template declaration。而且template array class是Array<T>而不是Array。

下面是个使用上述template class的例子

int main(){    Array<int> anArray(12);    Array<double> adArray(12);     for (int nCount = 0; nCount < 12; nCount++)    {        anArray[nCount] = nCount;        adArray[nCount] = nCount + 0.5;    }     for (int nCount = 11; nCount >= 0; nCount----;)        std::cout << anArray[nCount] << "\t" << adArray[nCount] << std::endl;     return 0;}

和template函数类似，template类也是在调用的时候由编译器实例化。