预备知识
- 模板参数可以是数值型参数(非类型参数)
template
< typename T, int N >
void func()
{
T a[N]; // 使用模板参数定义局部数组
}
func<double, 10>();
数值型模板参数的限制
- 变量不能作为模板参数
- 浮点数不能作为模板参数
- 类对象不能作为模板参数
- ......
本质:
模板参数是在编译阶段被处理的单元,因此,在编译阶段必须准确无误的唯一确定。
有趣的面试题:
用你觉得最高效的方法求 1 + 2 + 3 + ... + N 的值!
编程实验: 数值类模板参数
#include <iostream>
using namespace std;
template
< typename T, int N >
void func()
{
T a[N] = {0};
for(int i=0; i<N; i++)
{
a[i] = i;
}
for(int i=0; i<N; i++)
{
cout << a[i] << endl;
}
}
template
< int N >
class Sum
{
public:
static const int VALUE = Sum<N-1>::VALUE + N; // 编译器递归求值
};
template
< >
class Sum < 1 >
{
public:
static const int VALUE = 1;
};
int main()
{
cout << "1 + 2 + 3 + ... + 10 = " << Sum<10>::VALUE << endl;
cout << "1 + 2 + 3 + ... + 100 = " << Sum<100>::VALUE << endl;
return 0;
}
输出:
1 + 2 + 3 + ... + 10 = 55
1 + 2 + 3 + ... + 100 = 5050
编程实验: 数组模板类
Array.h
#ifndef _ARRAY_H_
#define _ARRAY_H_
template
< typename T, int N >
class Array
{
private:
T m_array[N];
public:
int length();
bool set(int index, T value);
bool get(int index, T& value);
T& operator[] (int index);
T operator[] (int index) const;
virtual ~Array(); // Array 类可能被继承,析构函数声明为虚函数
};
template
< typename T, int N >
int Array<T, N>::length()
{
return N;
}
template
< typename T, int N >
bool Array<T, N>::set(int index, T value)
{
bool ret = (index >=0) && (index < N);
if( ret )
{
m_array[index] = value;
}
return ret;
}
template
< typename T, int N >
bool Array<T, N>::get(int index, T& value)
{
bool ret = (index >=0) && (index < N);
if( ret )
{
value = m_array[index];
}
return ret;
}
template
< typename T, int N >
T& Array<T, N>::operator[] (int index)
{
return m_array[index];
}
template
< typename T, int N >
T Array<T, N>::operator[] (int index) const
{
return m_array[index];
}
template
< typename T, int N >
Array<T, N>::~Array()
{
}
#endif
main.cpp
#include <iostream>
#include "Array.h"
using namespace std;
int main()
{
Array<double, 5> ad;
for(int i=0; i<ad.length(); i++)
{
ad[i] = i * i;
}
for(int i=0; i<ad.length(); i++)
{
cout << ad[i] << endl;
}
return 0;
}
输出:
0
1
4
9
16
编程实验: 堆数组模板类
HeapArray.h
#ifndef _HEAPRRAY_H_
#define _HEAPARRAY_H_
template
< typename T >
class HeapArray
{
private:
int m_length;
T* m_pointer;
HeapArray(int len);
HeapArray(const HeapArray& obj);
bool construct();
public:
static HeapArray* NewInstance(int length);
int length();
bool get(int index, T& value);
bool set(int index, T value);
T& operator [] (int index);
T operator [] (int index) const;
HeapArray& operator = (const HeapArray& obj);
HeapArray& self();
~HeapArray();
};
template
< typename T >
HeapArray<T>::HeapArray(int len)
{
m_length = len;
}
template
< typename T >
bool HeapArray<T>::construct()
{
m_pointer = new T[m_length];
return m_pointer != NULL;
}
template
< typename T >
HeapArray<T>* HeapArray<T>::NewInstance(int length)
{
HeapArray<T>* ret = new HeapArray(length);
if( !(ret && (ret->construct())) )
{
delete ret;
ret = 0;
}
return ret;
}
template
< typename T >
int HeapArray<T>::length()
{
return m_length;
}
template
< typename T >
bool HeapArray<T>::get(int index, T& value)
{
bool ret = (index >= 0) && (index < length());
if( ret )
{
value = m_pointer[index];
}
return ret;
}
template
< typename T >
bool HeapArray<T>::set(int index, T value)
{
bool ret = (index >= 0) && (index < length());
if( ret )
{
m_pointer[index] = value;
}
return ret;
}
template
< typename T >
T& HeapArray<T>:: operator [] (int index)
{
return m_pointer[index];
}
template
< typename T >
T HeapArray<T>:: operator [] (int index) const
{
return m_pointer[index];
}
template
< typename T >
HeapArray<T>& HeapArray<T>:: operator = (const HeapArray<T>& obj)
{
if( this != &obj )
{
T* pointer = new T[obj.m_length];
if( pointer )
{
for(int i=0; i<obj.m_length; i++)
{
pointer[i] = obj.m_pointer[i];
}
m_length = obj.m_length;
delete m_pointer;
m_pointer = pointer;
}
}
return *this;
}
template
< typename T >
HeapArray<T>& HeapArray<T>::self()
{
return *this;
}
template
< typename T >
HeapArray<T>::~HeapArray()
{
delete[] m_pointer;
}
#endif
main.cpp
#include <iostream>
#include "HeapArray.h"
using namespace std;
int main()
{
HeapArray<char>* pai = HeapArray<char>::NewInstance(10);
if( pai != NULL )
{
HeapArray<char>& ai = pai->self();
for(int i=0; i<ai.length(); i++)
{
ai[i] = i + 'a';
}
for(int i=0; i<ai.length(); i++)
{
cout << ai[i] << endl;
}
}
delete pai;
return 0;
}
输出:
a
b
c
d
e
f
g
h
i
j
小结
- 模板参数可以是数值类型
- 数值型模板参数必须在编译期间唯一确定
- 数组类模板是基于数值型模板参数实现的
- 数组类模板是简易的线性表数据结构
以上内容参考狄泰软件学院系列课程,请大家保护原创!
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