C++ primer中的一道习题（16.12）,该怎么处理

C++ primer中的一道习题（16.12）
题目：
编写一个函数模版，接受表示未知类型迭代器的一对值，找出在序列中出现的最频繁的值。

该如何定义迭代器？

//16.12
#include<iostream>
#include<string>
#include<vector>
#include<list>
using namespace std;

template<typename T, typename V>
V most_occurs(typename T::const_iterator beg, typename T::const_iterator end)
{
typename T::size_type sz=0,max=0;
V tmp;
for(typename T::const_iterator it=beg; it!=end; ++it)
{
sz=count(beg,end,*it);
if(sz>max)
{
max=sz;
tmp=*it;
}
}

return tmp;
}

int main()
{
vector<int> vec;
int i;
for(i=0;i<10;++i)
vec.push_back(i);
vec.push_back(2);
vec.push_back(2);
vector<int>::const_iterator beg=vec.begin(), end=vec.end();
cout<<most_occurs(beg,end )<<endl;
return 0;
}

错误信息如下：
error C2783: 'V __cdecl most_occurs(generic-type-311,generic-type-312)' : could not deduce template argument for 'T'
error C2783: 'V __cdecl most_occurs(generic-type-311,generic-type-312)' : could not deduce template argument for 'V'

请问各位高手该如何定义该template？谢谢^_^

------解决方案--------------------

C/C++ code


#include <iostream> 
#include <string> 
#include <vector> 
#include <iterator>
#include <algorithm>
#include <list> 
using   namespace   std; 

template <typename   T>
typename  iterator_traits<T>::value_type most_occurs(   T  beg, T end )
{
    typename   iterator_traits<T>::difference_type   sz = 0,max = 0; 
    typename  iterator_traits<T>::value_type tmp; 
    for ( T  it = beg; it != end; ++it )
    {
        sz = count( beg, end, *it ); 
        if ( sz > max )
        {
            max = sz; 
            tmp = *it;
        }
    } 
    return   tmp;
} 

int main()
{
    vector <int> vec; 
    int i; 
    for ( i = 0; i < 10; ++i )
    {
        vec.push_back( i );
    } 
    vec.push_back( 2 ); 
    vec.push_back( 2 ); 
    vector <int> ::const_iterator   beg = vec. begin(), end = vec.end(); 
    cout << most_occurs( beg, end ) << endl; 
    return   0;
}

------解决方案--------------------

C/C++ code

template <typename T>
typename T::value_type mostFre(T first,T last)
{
    allocator<typename T::value_type>alloc;
    T newFirst=alloc.allocate(last-first);
    T newLast =newFirst +(last-first);
    std::uninitialized_copy(first,last,newFirst);
    std::sort (newFirst,newLast);
    std::size_t maxOccu =0,occ=0;
    T preIter =newFirst,maxOccuElemIt =newFirst;

    while(newFirst!=newLast)
    {
        if(*newFirst!=*preIter)
        {
            if(occu>maxOccu)
            {
                maxOccu=occu;
                maxOccuElemIt=preIter;
            }
            occu=0;
        }
        ++occu;
        preIter=newFirst;
        ++newFirst;
    }
    if(occu>maxOccu)
    {
        maxOccu=occu;
        maxOccuElemIt=preIter;
    }
    return *maxOccuElemIt;

}

------解决方案--------------------
最简单的做法:cout <<most_occurs<vector<int>,int>(beg,end) <<endl;  呵呵...
C++中要求在模板函数调用时，必须能够推导出参数类型(可以递归使用推导规则).
楼主的做法中，嵌套类型vector <int> ::const_iterator很明显不可能为其"外嵌"类型负责啦...

C++ primer中的一道习题（16.12）,该怎么处理

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