binary_search in c++ unexpected behaviour

Question

The following snippet is returning me 0. I expected it to be 1. What\'s wrong going on here?

#include 
#include 
#include 

        

Answer 1

Your array is not sorted, so binary_search got undefined behavior. Try std::find instead

bool found = std::find(v.begin(), v.end(), 10) != v.end()

§25.4.3.4 of the C++11 standard (3242 draft)

1. Requires: The elements e of [first,last) are partitioned with respect to the expressions e < value and !(value < e) or comp(e, value) and !comp(value, e). Also, for all elements e of [first, last), e < value implies !(value < e) or comp(e, value) implies !comp(value, e).