std::replace and std::replace_if in C++
Last Updated :
26 Apr, 2022
std::replace
Assigns new_value to all the elements in the range [first, last) that compare to old_value. The function use operator == to compare the individual elements to old_value
Function Template :
void replace (ForwardIterator first,
ForwardIterator last,
const T& old_value,
const T& new_value)
first, last :
Forward iterators to the initial and final positions
in a sequence of elements.
old_value : Value to be replaced.
new_value : Replacement value.
Return Value :
This function do not return any value. If elements that needs to be replace is found then element
replaced otherwise remain unchanged.
Examples:
Input : 10 20 30 30 20 10 10 20
Output : 10 99 30 30 99 10 10 99
// Replaced value 20 in vector to 99.
Input : 3 5 7 8 9 5 4
Output : 3 5 7 12 9 5 4
// Replaced value 8 by 12.
CPP
#include <bits/stdc++.h>
using namespace std;
int main()
{
int arr[] = { 10, 20, 30, 30, 20, 10, 10, 20 };
int n = sizeof (arr) / sizeof (arr[0]);
int old_val = 20, new_val = 99;
cout << "Original Array:" ;
for ( int i = 0; i < n; i++)
cout << ' ' << arr[i];
cout << '\n' ;
replace(arr, arr + n, old_val, new_val);
cout << "New Array:" ;
for ( int i = 0; i < n; i++)
cout << ' ' << arr[i];
cout << '\n' ;
return 0;
}
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Output
Original Array: 10 20 30 30 20 10 10 20
New Array: 10 99 30 30 99 10 10 99
std::replace_if
Assigns new_value to all the elements in range [first, last) for which pred returns true.
Function Template :
void replace_if (ForwardIterator first, ForwardIterator last,
UnaryPredicate pred, const T& new_value)
first, last : Forward iterators to the initial and final positions
in a sequence of elelments.
pred : Unary function that accepts an element in the range as argument, and
returns a value convertible to bool.The returned value indicate whether
the element is to be replaced (if true, it is replaced).
The function shall not modify its argument.
old_value : Value to be replaced.
new_value : Replacement value.
Examples:
Input : 1 2 3 4 5 6 7 8 9 10
Output : 0 2 0 4 0 6 0 8 0 10
// Replaced all odd values to 0.
Input : 10 20 30 30 20 10 10 20
Output : 10 4 30 30 4 10 10 4
// Replaced all number divisible by 4 to 4.
CPP
#include <bits/stdc++.h>
using namespace std;
bool IsOdd( int i)
{
return ((i % 2) == 1);
}
int main()
{
int arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
int n = sizeof (arr) / sizeof (arr[0]);
cout << "Original Array:" ;
for ( int i = 0; i < n; i++)
cout << ' ' << arr[i];
cout << '\n' ;
int new_val = 0;
replace_if(arr, arr + n, IsOdd, new_val);
cout << "New Array:" ;
for ( int i = 0; i < n; i++)
cout << ' ' << arr[i];
cout << '\n' ;
return 0;
}
|
Output
Original Array: 1 2 3 4 5 6 7 8 9 10
New Array: 0 2 0 4 0 6 0 8 0 10
Also you can add any kind of function in std::replace_if that can only have one argument only.
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