upper_bound and lower_bound in different headers?

Question

lower_bound doesn't give any error, but upper_bound does. On searching, it's present in <algorithm> headers file.

Why the inconsistency? would be interesting to know.

C++ code:

#include <iostream>                                                
#include <vector>     
using namespace std;                                               
int main() {                                                       
    vector<int> ans={1,5,7,8};                                     
    cout<< upper_bound(ans.begin(), ans.end(), 16) -ans.begin() <<endl;
    cout<< lower_bound(ans.begin(), ans.end(), 16) -ans.begin() <<endl;
    return 0;                                                      
}     

Output:

/tmp/a.cpp: In function ‘int main()’:
/tmp/a.cpp:7:50: error: ‘upper_bound’ was not declared in this scope
     cout<< upper_bound(ans.begin(), ans.end(), 16) <<endl;

EDIT

$ g++ -v
gcc version 5.2.1 20151010 (Ubuntu 5.2.1-22ubuntu2) 

Answer 1

When you include any std header, any and all symbols from std may be imported.

Basically, all you are guaranteed is that the symbols in the header you ask for will be available. Extra can come to.

So this is conforming.