C++ Algorithm Library - binary_search() Function

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Description

The C++ function std::algorithm::binary_search() tests whether value exists in sorted sequence or not. It use comp function for comparison.

Declaration

Following is the declaration for std::algorithm::binary_search() function form std::algorithm header.

C++98

template <class ForwardIterator, class T, class Compare>
bool binary_search (ForwardIterator first, ForwardIterator last, 
   const T& val, Compare comp);

Parameters

• first − Forward iterators to the initial positions of the searched sequence.

• last − Forward iterators to the final positions of the searched sequence.

• val − Value to search for in the range.

• comp − Binary function that accepts two arguments and returns a bool.

Return value

Returns true if value exists otherwise false.

Exceptions

Throws exception if either element comparison or an operation on an iterator throws exception.

Please note that invalid parameters cause undefined behavior.

Time complexity

Logarithmic in the distance between first and last.

Example

The following example shows the usage of std::algorithm::binary_search() function.

#include <iostream>
#include <vector>
#include <algorithm>
#include <string>

using namespace std;

bool comp(string s1, string s2) {
   return (s1 == s2);
}

int main(void) {
   vector<string> v = {"ONE", "Two", "Three"};
   bool result;

   result = binary_search(v.begin(), v.end(), "one", comp); 

   if (result == true)
      cout << "String \"one\" exist in vector." << endl;

   v[0] = "Ten";

   return 0;
}

Let us compile and run the above program, this will produce the following result −

String "one" exist in vector.