std::replace_copy, std::replace_copy_if

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 );

template< class InputIt, class OutputIt, class T >
constexpr OutputIt replace_copy( InputIt first, InputIt last, OutputIt d_first,
                                 const T& old_value, const T& new_value );

template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T >
ForwardIt2 replace_copy( ExecutionPolicy&& policy,
                         ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first,
                         const T& old_value, const T& new_value );

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 );

template< class InputIt, class OutputIt, class UnaryPredicate, class T >
constexpr OutputIt replace_copy_if( InputIt first, InputIt last,
                                    OutputIt d_first,
                                    UnaryPredicate p, const T& new_value );

template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,
          class UnaryPredicate, class T >
ForwardIt2 replace_copy_if( ExecutionPolicy&& policy,
                            ForwardIt1 first, ForwardIt1 last,
                            ForwardIt2 d_first,
                            UnaryPredicate p, const T& new_value );

Copies the elements from the range [first, last) to another range beginning at d_first, while replacing all elements satisfying specific criteria with new_value. If the source and destination ranges overlap, the behavior is undefined.

Parameters

Return value

Iterator to the element past the last element copied.

Complexity

Given N as std::distance(first, last):

Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
• If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation

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;
}

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;
}

Example

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
 
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';
}

5 99 4 2 99 99 1 99 0 3

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

1. The actual defect in the C++ standard is that the template parameter InputIterator was misspecified as Iterator. This affects the type requirements because the C++ standard states that for the function templates in the alrogithms library, the template type parameters whose name ends with Iterator imply the type requirements of the corresponding iterator categories.

See also