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# std::replace_copy, std::replace_copy_if

From cppreference.com
< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
template< class InputIt, class OutputIt, class T > OutputIt replace_copy( InputIt first, InputIt last, OutputIt d_first, const T& old_value, const T& new_value ); | (1) |
template< class InputIt, class OutputIt, class UnaryPredicate, class T > OutputIt replace_copy_if( InputIt first, InputIt last, OutputIt d_first, UnaryPredicate p, const T& new_value ); | (2) |

Copies the all elements from the range `[first, last)` to another range beginning at `d_first` replacing all elements satisfying specific criteria with `new_value`. The first version replaces the elements that are equal to `old_value`, the second version replaces elements for which predicate `p` returns true. The source and destination ranges cannot overlap.

### [edit] Parameters

first, last | - | the range of elements to copy
d_first | - | the beginning of the destination range
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 InputIt can be dereferenced and then implicitly converted to Type. ​
new_value | - | the value to use as replacement
Type requirements
- `InputIt` must meet the requirements of `InputIterator`.
- `OutputIt` must meet the requirements of `OutputIterator`.

### [edit] Return value

Iterator to the element past the last element copied.

### [edit] Complexity

Exactly `last - first` applications of the predicate.

### [edit] Possible implementation

First version
    template<class InputIt, class OutputIt, class T>
    OutputIt replace_copy(InputIt first, InputIt last, OutputIt d_first,
                          const T& old_value, const T& new_value)
    {
        for (; first != last; ++first) {
            *d_first++ = (*first == old_value) ? new_value : *first;
        }
        return d_first;
    }
Second version
    template<class InputIt, class OutputIt,
             class UnaryPredicate, class T>
    OutputIt replace_copy_if(InputIt first, InputIt last, OutputIt d_first,
                             UnaryPredicate p, const T& new_value)
    {
        for (; first != last; ++first) {
            *d_first++ = p( *first ) ? new_value : *first;
        }
        return d_first;
    }

### [edit] Example

The following copy prints a vector, replacing all values over 5 with 99 on the fly.

Run this code

    #include <algorithm>
    #include <vector>
    #include <iostream>
    #include <iterator>
    #include <functional>

    int main()
    {
        std::vector<int> v{5, 7, 4, 2, 8, 6, 1, 9, 0, 3};
        std::replace_copy_if(v.begin(), v.end(),
                             std::ostream_iterator<int>(std::cout, " "),
                             [](int n){return n > 5;}, 99);
        std::cout << '\n';
    }

Output:

    5 99 4 2 99 99 1 99 0 3

### [edit] See also

remove remove_if | removes elements satisfying specific criteria (function template) [edit]

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