How to use the search() function in C++

The search() function in C++ helps search for a sequence of elements inside an array/vector. This function is available in the <algorithm.h> header file.

Parameters

The search() function accepts the following parameters:

  • first1, last1: These are the iterators pointing to the initial and final positions of the array/vector where the search operation needs to be performed.

  • first2, last2: These are the iterators pointing to the initial and final positions of the array/vector that needs to be searched.

  • pred: This is an optional parameter that specifies a binary function that returns a boolean value, which indicates how to perform the search.

Return value

The search() function returns an iterator that points to the first occurrence of the sequence in the range [first2, last2) in the sequence [first1, last1). If the value is not found, then it returns an iterator to last1 of the array or vector.

Code

Let’s take a look at the code.

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main () {
  vector<int> vec;
  for (int i = 1; i <= 10; i++) 
    vec.push_back(i*10);
  int seq[] = {40,50,60,70};
  auto it = search(vec.begin(), vec.end(), seq, seq + 4);
  if (it!=vec.end())
    cout << "Sequence found at position " << (it-vec.begin());
  else
    cout << "Sequence not found";  
  return 0;
}

Explanation

  • In lines 1 to 3, we import the required libraries.
  • In lines 7 to 9, we create a vector with some integer values.
  • In line 11, we define the sequence that we want to search in the vector.
  • In line 12, we call the search() function and pass all the required parameters.
  • In line 14, we check whether the sequence is found or not. If the sequence is not found, then the value of it points to the end of the vector.
  • In line 15, we print the index from where the sequence starts.
  • In line 17, we print if the sequence is not found.

Now, let us look at code where we use a binary predicate to perform the search.

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
bool pred (int i, int j) {
  return (i==j);
}
int main() {
  
  vector<int> vec;
  for (int i = 1; i <= 10; i++) 
    vec.push_back(i*10);
  
  int seq[] = {20,30,50};
  auto it = search (vec.begin(), vec.end(), seq, seq + 3, pred);
  if (it!=vec.end())
    cout << "Sequence found at position " << (it-vec.begin());
  else
    cout << "Sequence not found";
  return 0;
}

Explanation

  • In lines 1 to 3, we import the required libraries.
  • In lines 6 to 8, we create a binary function that accepts two integers and returns a boolean value.
  • In lines 12 to 14, we create a vector with some integer values.
  • In line 16, we define the sequence that we want to search in the vector.
  • In line 15, we call the search() function and pass all the required parameters.
  • In line 19, we check whether the sequence is found or not. If the sequence is not found, then the value of it points to the end of the vector.
  • In line 20, we print the index from where the sequence starts.
  • In line 22, we print if the sequence is not found.

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