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std::replace_copy_if() algorithm

// (1)
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 );

// (2)
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 );
  • (1) Copies the elements from the range [first; last) to another range beginning at d_first, while replacing elements that satisfy prediate p 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.

Parameters

first
last

The range of elements to copy.

d_first

The beginning of the destination range.

policy

The execution policy to use. See execution policy for details.

p

Unary predicate which returns true if the element should be replaced.

The expression p(v) must be convertible to bool for every argument v of type (possibly const) VT, where VT is the value type of InputIt, regardless of value category, and must not modify v. Thus, a parameter type of VT& is not allowed , nor is VT unless for VT a move is equivalent to a copy. (od C++11).

Type requirements

InputItLegacyInputIterator
OutputItLegacyOutputIterator
ForwardIt1
ForwardIt2
LegacyForwardIterator
PredicateUnaryPredicate

The results of the 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 applications of the predicate p.

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_if (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)
{
for (; first != last; ++first)
*d_first++ = p(*first) ? 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_if() algorithm

// (1)
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 );

// (2)
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 );
  • (1) Copies the elements from the range [first; last) to another range beginning at d_first, while replacing elements that satisfy prediate p 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.

Parameters

first
last

The range of elements to copy.

d_first

The beginning of the destination range.

policy

The execution policy to use. See execution policy for details.

p

Unary predicate which returns true if the element should be replaced.

The expression p(v) must be convertible to bool for every argument v of type (possibly const) VT, where VT is the value type of InputIt, regardless of value category, and must not modify v. Thus, a parameter type of VT& is not allowed , nor is VT unless for VT a move is equivalent to a copy. (od C++11).

Type requirements

InputItLegacyInputIterator
OutputItLegacyOutputIterator
ForwardIt1
ForwardIt2
LegacyForwardIterator
PredicateUnaryPredicate

The results of the 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 applications of the predicate p.

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_if (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)
{
for (; first != last; ++first)
*d_first++ = p(*first) ? 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.