C++ <algorithm> - generate_n() Function

The C++ algorithm::generate_n function is used to assign value returned by successive calls of function gen to the first n elements of the sequence pointed by first.

Syntax

• C++98
• C++11

template <class OutputIterator, class Size, class Generator>
  void generate_n (OutputIterator first, 
                   Size n, 
                   Generator gen);

template <class OutputIterator, class Size, class Generator>
  OutputIterator generate_n (OutputIterator first, 
                             Size n, 
                             Generator gen);

Parameters

Return Value

Returns an iterator pointing to the element that follows the last element whose value has been assigned or None(in C++98).

Time Complexity

Linear i.e, Θ(n).

Example:

In the example below, the algorithm::generate_n function is used to assign value in the given sequence using specified generator function.

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std; 

int N = 1;
int gen() {
  return 10*(N++);
} 

int main (){
  vector<int> vec{1, 1, 1, 1, 1};
  vector<int>::iterator it;

  cout<<"Before generate_n call, vec contains:";
  for(it = vec.begin(); it != vec.end(); ++it)
    cout<<" "<<*it;

  //assign values to the vector
  generate_n(vec.begin(), 3, gen);

  cout<<"\nAfter generate_n call, vec contains:";
  for(it = vec.begin(); it != vec.end(); ++it)
    cout<<" "<<*it;

  return 0;
}

The output of the above code will be:

Before generate_n call, vec contains: 1 1 1 1 1
After generate_n call, vec contains: 10 20 30 1 1