二進制搜索C++ STL

Question

我有一個unordered_map矢量，它是根據我定義的比較函數排序的。我想使用二進制搜索來使用比較器函數來查找其中的一個值。然而，二分查找只返回布爾，我需要結果的索引/迭代器。我能做什麼？

Answer 1

#include <algorithm> 
using namespace std; 

//!!!!! a must be sorted using cmp. Question indicates that it is.   
it = lower_bound(a.begin, a.end(), value, cmp); 

//Check that we have actually found the value. 
//If the requested value is missing 
//then we will have the value before where the requested value 
//would be inserted. 
if(it == a.end() || !cmp(*it, value)) 
{ 
    //element not found 
} 
else 
{ 
    //element found 
} 

Answer 2

#include <algorithm> 
using namespace std; 

it = lower_bound(a.begin, a.end(), value, cmp);