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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（我还包括了我正在使用的排序谓词）。我知道小于默认值。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;
};

执行

    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，但是如果我这样尝试使用 std::find_if

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

以上工作。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。链接器错误是：

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 10.0\vc\include\algorithm    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 10.0\vc\include\algorithm    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 10.0\vc\include\algorithm    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 10.0\vc\include\algorithm    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 10.0\vc\include\algorithm    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 10.0\vc\include\algorithm    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 10.0\vc\include\algorithm    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 10.0\vc\include\algorithm    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 10.0\vc\include\algorithm    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 10.0\vc\include\algorithm    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 10.0\vc\include\algorithm    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 10.0\vc\include\algorithm    2978    1
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1 回答 1

2

该binary_search函数不采用等式运算符，而是采用定义顺序的不等式迭代器。您必须将谓词建模为小于比较。

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来决定继续搜索的方向。pred(*it,value)当两者都不为真时，该元素被认为是找到pred(value,*it)的（如果两个值都不小于另一个，则它们是相同的）

于 2013-11-04T16:15:38.860 回答