std::replace_copy() algorithm

since C++20

// (1)
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 );

// (2)
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 );

since C++17

// (1)
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 );

// (2)
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 );

until C++17

// (1)
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) Copies the elements from the range [first; last) to another range beginning at d_first, while replacing elements equal to old_value with new_value (compared using operator==).

• (2) Same as (1), but executed according to policy.

  Overload Resolution

  These overloads participate in overload resolution only if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>  (until C++20) std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>  (since C++20) is true.

Undefined Behaviour

If source and destination ranges overlap, the behavior is undefined

.

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.
new_value	The value to use as a replacement.
policy	The execution policy to use. See execution policy for details.

Type requirements

InputIt	LegacyInputIterator
OutputIt	LegacyOutputIterator
ForwardIt1 ForwardIt2	LegacyForwardIterator

The results of expressions *first and new_value must be writable to d_first.

Return value

Iterator to the element past the last element copied.

Complexity

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

Exactly N comparisons with old_value using operator==.

important

For the overloads with an ExecutionPolicy, there may be a performance cost if ForwardIt1's value_type is not MoveConstructible.

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

replace_copy (1)

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;
}

Examples

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

Main.cpp

#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';
}

Output

5 99 4 2 99 99 1 99 0 3