Przejdź do głównej zawartości

std::partition_copy() algorithm

// (1)
template< class InputIt, class OutputIt1,
class OutputIt2, class UnaryPredicate >
constexpr std::pair<OutputIt1, OutputIt2>
partition_copy( InputIt first, InputIt last,
OutputIt1 d_first_true, OutputIt2 d_first_false,
UnaryPredicate p );

// (2)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,
class ForwardIt3, class UnaryPredicate >
std::pair<ForwardIt2, ForwardIt3>
partition_copy( ExecutionPolicy&& policy,
ForwardIt1 first, ForwardIt1 last,
ForwardIt2 d_first_true, ForwardIt3 d_first_false,
UnaryPredicate p );
  • (1) Copies the elements from the range [first; last) to two different ranges depending on the value returned by the predicate p.

    The elements that satisfy the predicate p are copied to the range beginning at d_first_true. The rest of the elements are copied to the range beginning at d_first_false.

    Undefined Behaviour

    The behavior is undefined

    if the input range overlaps either of the output ranges.

  • (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 from.

d_first_true

The beginning of the output range for the elements that satisfy p

d_first_false

The beginning of the output range for the elements that don't satisfy p

policy

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

p

Unary predicate which returns true for the required element.

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
Dereferenced InputIt CopyAssignable
OutputIt1
OutputIt2
LegacyOutputIterator
ForwardIt1
ForwardIt2
ForwardIt3
LegacyForwardIterator
UnaryPredicatePredicate

ForwardIt1::value_type must be:

Return value

A std::pair constructed from the iterator to the end of the d_first_true range and the iterator to the end of the d_first_false range.

Complexity

Exactly std::distance(first, last) applications of p.

For the overload with an ExecutionPolicy, there may be a performance cost if ForwardIt's value type is not CopyConstructible.

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

partition_copy (1)
template<class InputIt, class OutputIt1,
class OutputIt2, class UnaryPredicate>
std::pair<OutputIt1, OutputIt2>
partition_copy(InputIt first, InputIt last,
OutputIt1 d_first_true, OutputIt2 d_first_false,
UnaryPredicate p)
{
for (; first != last; ++first)
{
if (p(*first))
{
*d_first_true = *first;
++d_first_true;
}
else
{
*d_first_false = *first;
++d_first_false;
}
}

return std::pair<OutputIt1, OutputIt2>(d_first_true, d_first_false);
}

Examples

Main.cpp
#include <algorithm>
#include <iostream>
#include <utility>

void print(auto rem, auto const& v)
{
for (std::cout << rem; auto const& x : v)
std::cout << x << ' ';
std::cout << '\n';
}

int main()
{
int arr[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
int true_arr[5] = {0};
int false_arr[5] = {0};

std::partition_copy(std::begin(arr), std::end(arr),
std::begin(true_arr), std::begin(false_arr),
[](int i) { return 4 < i; });

print("true_arr: ", true_arr);
print("false_arr: ", false_arr);
}
Output
true_arr:  5 6 7 8 9
false_arr: 0 1 2 3 4
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.

std::partition_copy() algorithm

// (1)
template< class InputIt, class OutputIt1,
class OutputIt2, class UnaryPredicate >
constexpr std::pair<OutputIt1, OutputIt2>
partition_copy( InputIt first, InputIt last,
OutputIt1 d_first_true, OutputIt2 d_first_false,
UnaryPredicate p );

// (2)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,
class ForwardIt3, class UnaryPredicate >
std::pair<ForwardIt2, ForwardIt3>
partition_copy( ExecutionPolicy&& policy,
ForwardIt1 first, ForwardIt1 last,
ForwardIt2 d_first_true, ForwardIt3 d_first_false,
UnaryPredicate p );
  • (1) Copies the elements from the range [first; last) to two different ranges depending on the value returned by the predicate p.

    The elements that satisfy the predicate p are copied to the range beginning at d_first_true. The rest of the elements are copied to the range beginning at d_first_false.

    Undefined Behaviour

    The behavior is undefined

    if the input range overlaps either of the output ranges.

  • (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 from.

d_first_true

The beginning of the output range for the elements that satisfy p

d_first_false

The beginning of the output range for the elements that don't satisfy p

policy

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

p

Unary predicate which returns true for the required element.

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
Dereferenced InputIt CopyAssignable
OutputIt1
OutputIt2
LegacyOutputIterator
ForwardIt1
ForwardIt2
ForwardIt3
LegacyForwardIterator
UnaryPredicatePredicate

ForwardIt1::value_type must be:

Return value

A std::pair constructed from the iterator to the end of the d_first_true range and the iterator to the end of the d_first_false range.

Complexity

Exactly std::distance(first, last) applications of p.

For the overload with an ExecutionPolicy, there may be a performance cost if ForwardIt's value type is not CopyConstructible.

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

partition_copy (1)
template<class InputIt, class OutputIt1,
class OutputIt2, class UnaryPredicate>
std::pair<OutputIt1, OutputIt2>
partition_copy(InputIt first, InputIt last,
OutputIt1 d_first_true, OutputIt2 d_first_false,
UnaryPredicate p)
{
for (; first != last; ++first)
{
if (p(*first))
{
*d_first_true = *first;
++d_first_true;
}
else
{
*d_first_false = *first;
++d_first_false;
}
}

return std::pair<OutputIt1, OutputIt2>(d_first_true, d_first_false);
}

Examples

Main.cpp
#include <algorithm>
#include <iostream>
#include <utility>

void print(auto rem, auto const& v)
{
for (std::cout << rem; auto const& x : v)
std::cout << x << ' ';
std::cout << '\n';
}

int main()
{
int arr[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
int true_arr[5] = {0};
int false_arr[5] = {0};

std::partition_copy(std::begin(arr), std::end(arr),
std::begin(true_arr), std::begin(false_arr),
[](int i) { return 4 < i; });

print("true_arr: ", true_arr);
print("false_arr: ", false_arr);
}
Output
true_arr:  5 6 7 8 9
false_arr: 0 1 2 3 4
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.