我的代码中的binary_search谓词有什么问题

What is wrong with the binary_search predicate in my code

本文关键字：谓词 什么 问题 search 代码 binary 我的      更新时间：2023-10-16

我正在阅读有关binary_search的信息，然后我尝试使用谓词来实现它。这是我的代码（我还包含了我正在使用的排序谓词）。我知道小于是默认值。这是粗略的测试代码

class person
{
public:
    int age;
};
//sort predicate
class less_than_key
{
public:
    inline bool operator()(const person& pa , const person& pb)
    {
        return (pa.age < pb.age);
    }
};
//Binary Search predicate
class bsearch_predicate
{
    public:
    bool operator()(const person& pa)
    {
        return pa.age == n;
    }
    bsearch_predicate(int i):n(i) {}
    int n;
};

实现

    person p;
p.age = 24;
std::vector<person> vec;
vec.push_back(p);
std::sort(vec.begin(),vec.end(),less_than_key());
std::binary_search(vec.begin(),vec.end(),bsearch_predicate(24));

现在这里的binary_search会产生错误，但是如果我尝试使用 std：：find_if

std::find_if(vec.begin(),vec.end(),bsearch_predicate(24));

以上作品。如果有人能告诉我为什么我的代码中出现 std：：binary_search 的链接器错误，我将不胜感激。链接器错误包括：

Error   12  error C2676: binary '<' : 'const bsearch_predicate' does not define this operator or a conversion to a type acceptable to the predefined operator   d:program files (x86)microsoft visual studio 10.0vcincludealgorithm    2978    1
Error   4   error C2784: 'bool std::operator <(const _Elem *,const std::basic_string<_Elem,_Traits,_Alloc> &)' : could not deduce template argument for 'const _Elem *' from 'const bsearch_predicate'  d:program files (x86)microsoft visual studio 10.0vcincludealgorithm    2978    1
Error   10  error C2784: 'bool std::operator <(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2> &)' : could not deduce template argument for 'const std::_Revranit<_RanIt,_Base> &' from 'const bsearch_predicate' d:program files (x86)microsoft visual studio 10.0vcincludealgorithm    2978    1
Error   7   error C2784: 'bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)' : could not deduce template argument for 'const std::_Tree<_Traits> &' from 'const bsearch_predicate'  d:program files (x86)microsoft visual studio 10.0vcincludealgorithm    2978    1
Error   3   error C2784: 'bool std::operator <(const std::basic_string<_Elem,_Traits,_Alloc> &,const _Elem *)' : could not deduce template argument for 'const std::basic_string<_Elem,_Traits,_Alloc> &' from 'const bsearch_predicate'    d:program files (x86)microsoft visual studio 10.0vcincludealgorithm    2978    1
Error   5   error C2784: 'bool std::operator <(const std::basic_string<_Elem,_Traits,_Alloc> &,const std::basic_string<_Elem,_Traits,_Alloc> &)' : could not deduce template argument for 'const std::basic_string<_Elem,_Traits,_Alloc> &' from 'const bsearch_predicate'  d:program files (x86)microsoft visual studio 10.0vcincludealgorithm    2978    1
Error   1   error C2784: 'bool std::operator <(const std::list<_Ty,_Ax> &,const std::list<_Ty,_Ax> &)' : could not deduce template argument for 'const std::list<_Ty,_Ax> &' from 'const bsearch_predicate' d:program files (x86)microsoft visual studio 10.0vcincludealgorithm    2978    1
Error   2   error C2784: 'bool std::operator <(const std::move_iterator<_RanIt> &,const std::move_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::move_iterator<_RanIt> &' from 'const bsearch_predicate'    d:program files (x86)microsoft visual studio 10.0vcincludealgorithm    2978    1
Error   11  error C2784: 'bool std::operator <(const std::pair<_Ty1,_Ty2> &,const std::pair<_Ty1,_Ty2> &)' : could not deduce template argument for 'const std::pair<_Ty1,_Ty2> &' from 'const bsearch_predicate'   d:program files (x86)microsoft visual studio 10.0vcincludealgorithm    2978    1
Error   9   error C2784: 'bool std::operator <(const std::reverse_iterator<_RanIt> &,const std::reverse_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::reverse_iterator<_RanIt> &' from 'const bsearch_predicate'   d:program files (x86)microsoft visual studio 10.0vcincludealgorithm    2978    1
Error   8   error C2784: 'bool std::operator <(const std::unique_ptr<_Ty,_Dx> &,const std::unique_ptr<_Ty2,_Dx2> &)' : could not deduce template argument for 'const std::unique_ptr<_Ty,_Dx> &' from 'const bsearch_predicate' d:program files (x86)microsoft visual studio 10.0vcincludealgorithm    2978    1
Error   6   error C2784: 'bool std::operator <(const std::vector<_Ty,_Ax> &,const std::vector<_Ty,_Ax> &)' : could not deduce template argument for 'const std::vector<_Ty,_Ax> &' from 'const bsearch_predicate'   d:program files (x86)microsoft visual studio 10.0vcincludealgorithm    2978    1

binary_search 函数不接受相等运算符，而是采用定义顺序的不等式迭代器。您必须对谓词进行建模，就好像它是一个小于比较一样。

原因是binary_search算法需要知道参数的相对顺序和它正在查看的元素，以决定继续搜索的方向。当pred(*it,value)和pred(value,*it)都不为真时，将认为已找到该元素（如果两个值都不小于另一个值，则它们是相同的）

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