對向量中的查找函數中的錯誤

Question

在此函數中，我搜索向量緩存中的pair.first。矢量是：

vector<pair<double,unsigned int> > cache; 

我已經使用查找功能自定義功能：

struct comp 
{ 
    comp(double const& s) : _s(s) { } 

    bool operator() (pair<double, unsigned int> const& p) 
    { 
     return (p.first == _s); 
    } 

    double _s; 
}; 

我打電話查找功能：

it = find(cache.begin(),cache.end(),comp(value)); 

在編譯時，我得到一個很多錯誤。前幾行是：

In file included from /usr/include/c++/4.6/algorithm:63:0, from my_class.hpp:5, from main.cpp:5: /usr/include/c++/4.6/bits/stl_algo.h: In function ‘RandomAccessIterator std::_find(_RandomAccessIterator, _RandomAccessIterator, const _Tp&, std::random_access_iterator_tag) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator*, std::vector > >, _Tp = MyCode::MyClass::comp]’: /usr/include/c++/4.6/bits/stl_algo.h:4326:45: instantiated from ‘_IIter std::find(_IIter, _IIter, const _Tp&) [with _IIter = __gnu_cxx::__normal_iterator*, std::vector > >, _Tp = MyCode::MyClass::comp]’ my_class.hpp:76:53: instantiated from here /usr/include/c++/4.6/bits/stl_algo.h:162:4: error: no match for ‘operator==’ in ‘_first._gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* with _Iterator = std::pair*, _Container = std::vector >, __gnu_cxx::__normal_iterator<_Iterator, _Container>::reference = std::pair& == __val’

我該如何解決這個錯誤？

Answer 1

您傳遞的是一個謂詞，而不是一個值，所以您需要find_if()而不是find()。

Answer 2

您的電話應該使用std::find_if，而不是std::find。

it = find_if(cache.begin(),cache.end(),comp(value)); 
if (it != cache.end()) 
{ 


}