std::replace, std::replace_if

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Defined in header <algorithm>

template< class ForwardIterator, class T >

void replace( ForwardIterator first, ForwardIterator last,

              const T& old_value, const T& new_value );
(1)
template< class ForwardIterator, class UnaryPredicate, class T >

void replace_if( ForwardIterator first, ForwardIterator last,

                 UnaryPredicate p, const T& new_value );
(2)

Replaces all elements satisfying specific criteria with new_value in the range [first, last). The first version replaces the elements that are equal to old_value, the second version replaces elements for which predicate p returns true.

Contents

[edit] Parameters

first, last - the range of elements to process
old_value - the value of elements to replace
p - unary predicate which returns ​true if the element value should be replaced.

The signature of the predicate function should be equivalent to the following:

bool pred(const Type &a);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The type Type must be such that an object of type ForwardIterator can be dereferenced and then implicitly converted to Type. ​

new_value - the value to use as replacement

[edit] Return value

(none)

[edit] Complexity

Exactly last - first applications of the predicate.

[edit] Equivalent function

[edit] Example

The following code at first replaces all occurrences of 8 with 88 in a vector of integers. Then it replaces all values less than 5 with 55.

#include <algorithm>
#include <array>
#include <iostream>
#include <functional>
 
int main()
{
    std::array<int, 10> s{5, 7, 4, 2, 8, 6, 1, 9, 0, 3};
 
    std::replace(s.begin(), s.end(), 8, 88);
 
    for (int a : s) {
        std::cout << a << " ";
    }
    std::cout << '\n';
 
    std::replace_if(s.begin(), s.end(), 
                    std::bind(std::less<int>(), std::placeholders::_1, 5), 55);
    for (int a : s) {
        std::cout << a << " ";
    }
    std::cout << '\n';
}

Output:

5 7 4 2 88 6 1 9 0 3
5 7 55 55 99 6 55 9 55 55

[edit] See also

replace_copy
replace_copy_if
copies a range, replacing elements satisfying specific criteria with another value
(function template)