涉及std :: equal_range的无效操作数编译器错误 [英] Invalid operand compiler error involving std::equal_range

问题描述

对于使用以下模板的间隔图的实现

For an implementation of an interval map using the following template

template<class K, class V>
intervalMap{
public:
intervalMap(V const&);
public:
void assign(K const&, K const&, V const&);
private:
std::map<K,V>m_map;
};

以及成员函数 assign（）：

template<class K, class V> void intervalMap::assign(
                                             K const& keyBegin, 
                                             K const& keyEnd,
                                             V const& val
                                            ){

            auto begin = m_map.find(keyBegin);
            auto end = m_map.find(keyEnd);

            auto p = std::equal_range(begin,end,val);

}

以及以下main（）实例化

and the following instantiation in main()

intervalMap<unsigned int, char> iMap('A');
iMap.assign(1,2,'A');

以下编译错误结果：

In file included from main.cpp:1:
In file included from ./code.hpp:4:
In file included from /Library/Developer/CommandLineTools/usr/
include/c++/v1/map:442:
In file included from /Library/Developer/CommandLineTools/usr
/include/c++/v1/__tree:18:
/Library/Developer/CommandLineTools/usr/include/
c++/v1/algorithm:701:71: 
error: invalid operands to binary expression 
('const std::__1::pair<const unsigned int, char>' and 'int')
    bool operator()(const _T1& __x, const _T2& __y) 
const {return __x < __y;}
              ~~~ ^ ~~~

该错误与以下来源有关代码段（在错误日志中突出显示）：

The error pertains to the following source code segment (as highlighted in the error log):

./code.hpp:120:18: note: in instantiation of function 
template specialization 'std::__1::equal_range
<std::__1::__map_iterator
<std::__1::__tree_iterator
<std::__1::__value_type
<unsigned int, char>, 
std::__1::__tree_node
<std::__1::__value_type
<unsigned int, char>, 
void *> *, long> >, 
char>' 
requested here
        auto p = equal_range(begin,end,val);
                 ^
./code.hpp:205:10: note: 
in instantiation of member function 
'interval_map<unsigned int, char>::assign' 
requested here
    iMap.assign(1,2,'A');

很不错的建议。

推荐答案

错误是由于将std :: pair和以V表示的模板变量（在本例中为char）进行比较而引起的。为避免这种情况，可以使用如下的服装谓词。

error is due to comparing std::pair and template variable denoted by V, in this case char. To avoid this you can use costume predicate as below.

template<class K, class V>
class intervalMap{
public:
intervalMap(V  val)
{
   v = val;
}
public:
void assign(K const a, const K  b,  const V c);

private:
V v;
std::map<K,V> m_map;

};
template<class K, class V>
struct comp
{
    bool operator()(std::pair<K, V> a, V b)
    {
        return a.second < b;
    }
    bool operator()(V a, std::pair<K, V> b)
    {
        return a < b.second;
    }
};

template<class K, class V>
void intervalMap<K, V>::assign(const K  keyBegin, const K  keyEnd, const V  
val)
{
    auto begin = m_map.find(keyBegin);
    auto end = m_map.find(keyEnd);


    auto p = std::equal_range(begin, end, val,comp< K,  V>());
}

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