C++ <algorithm> - replace_copy_if() Function

The C++ algorithm::replace_copy_if function is used to copy all elements in the range [first, last) to the range starting at result, with all values replaced by new_value for which pred returns true.

Syntax

template <class InputIterator, class OutputIterator, class UnaryPredicate, class T>
  OutputIterator replace_copy_if (InputIterator first, InputIterator last,
                                  OutputIterator result, UnaryPredicate pred,
                                  const T& new_value);

Parameters

`first`	Specify initial position of the input iterator. The range used is [first,last).
`last`	Specify final position of the input iterator. The range used is [first,last).
`result`	Specify initial position of the output iterator where the result to be stored.
`pred`	Specify an unary function that accepts an element in the range as argument, and returns a value convertible to bool. The element will be replaced if the function returns true.
`new_value`	Specify the value to replaced with.

Return Value

Returns an iterator pointing to the element that follows the last element replaced in result sequence.

Time Complexity

Linear i.e, Θ(n).

Example:

In the example below, the algorithm::replace_copy_if function is used to copy all elements of an array to a vector, with all odd elements replaced by 0.

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
 
bool isOdd (int i) {return (i%2==1);}

int main (){
  int arr[] = {10, 11, 12, 13, 14, 15};
  vector<int> vec(6);
  vector<int>::iterator it;

  //copy elements from array to vector and 
  //replace all odd numbers by 0
  replace_copy_if(arr, arr+6, vec.begin(), isOdd, 0);

  cout<<"arr contains:";
  for(int i = 0; i < 6; ++i)
    cout<<" "<<arr[i];

  cout<<"\nvec contains:";
  for(it = vec.begin(); it != vec.end(); ++it)
    cout<<" "<<*it;

  return 0;
}

The output of the above code will be:

arr contains: 10 11 12 13 14 15
vec contains: 10 0 12 0 14 0

❮ C++ <algorithm> Library