Essential c++阅读笔记-第3章 数组和vector的find方法(哨兵指针)

#include <iostream>
#include <vector>
#include <string>
using std::cout;
using std::endl;
using std::vector;
using std::string;


#define arr_size 5
//vector模版，vector引用形参
template<typename T>
const T* find(const vector<T> &vec,int &value)
{
    for(vector<typename T>::size_type i=0;i<vec.size();++i)
    {
        if(vec[i]==value)
          return &vec[i];
    }
    return 0;
}
//数组指针
template<typename T>
const T* find1(const T *arr,int size,const T &value)
{
    if(!arr || size<1)//检查空指针和空元素
        return 0;//返回空指针
    for(int ix=0;ix<size;++ix)
    {
        if(arr[ix]==value)
            return &arr[ix];
    }
    return 0;
}
//数组指针加结束(哨兵)指针，类似于迭代器，通过指针算术操作来得到哨兵指针
template<typename T>
const T* find2(const T *arr,const T *end,const T &value)
{
    if(!arr || !end)
        return 0;
    for(;arr!=end;++arr)
    {
        if(*arr==value)
            return arr;
    }
    return 0;
}

int main()
{
    vector<int> vec;
    vec.push_back(1);
    vec.push_back(2);
    vec.push_back(3);
    vec.push_back(4);
    vec.push_back(2);
    int val=2;
    const int *p=find(vec,val);
    cout<<"find:"<<(p==0?0:*p)<<endl;
    int arr[arr_size]={1,2,3,4,5};
    p=find1(arr,arr_size,val);
    cout<<"find1(int array):"<<(p==0?0:*p)<<endl;
    string str[arr_size]={"kenny","hello","abc","jay","hi"};
    string val_str("hello");
    const string *pstr=find1(str,arr_size,val_str);
    cout<<"find1(string array):"<<(pstr==0?"null":*pstr)<<endl;
    p=find2(arr,arr+5,val);
    cout<<"find2(int array):"<<(p==0?0:*p)<<endl;
    pstr=find2(str,str+5,val_str);
    cout<<"find2(string array):"<<(pstr==0?"null":*pstr)<<endl;
    system("PAUSE");
    return 0;
}