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std::replace_copy() algorithm

// (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 );
  • (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>>  (do C++20) std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>  (od 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

InputItLegacyInputIterator
OutputItLegacyOutputIterator
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
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std::replace_copy() algorithm

// (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 );
  • (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>>  (do C++20) std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>  (od 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

InputItLegacyInputIterator
OutputItLegacyOutputIterator
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
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.