Namespaces
Variants
Views
Actions

Difference between revisions of "cpp/algorithm/remove copy"

From cppreference.com
< cpp‎ | algorithm
m (→‎Example: + lost new line)
m (FTM.)
 
(11 intermediate revisions by 3 users not shown)
Line 1: Line 1:
−
{{cpp/title|remove_copy | remove_copy_if}}
+
{{cpp/title|remove_copy|remove_copy_if}}
 
{{cpp/algorithm/navbar}}
 
{{cpp/algorithm/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
−
{{dcl header | algorithm}}
+
{{dcl header|algorithm}}
−
{{dcl rev multi | num=1 | since1= | until1=c++20 |dcl1=
+
{{dcl rev begin|num=1}}
 +
{{dcla|anchor=1|constexpr=c++20|until=c++26|
 
template< class InputIt, class OutputIt, class T >
 
template< class InputIt, class OutputIt, class T >
−
OutputIt remove_copy( InputIt first, InputIt last, OutputIt d_first,
+
OutputIt remove_copy( InputIt first, InputIt last,
−
                      const T& value );
+
                      OutputIt d_first, const T& value );
−
|dcl2=
+
}}
−
template< class InputIt, class OutputIt, class T >
+
{{dcl|since=c++26|1=
−
constexpr OutputIt remove_copy( InputIt first, InputIt last, OutputIt d_first,
+
template< class InputIt, class OutputIt,
−
                                const T& value );
+
          class T = typename std::iterator_traits
 +
                        <InputIt>::value_type >
 +
constexpr OutputIt remove_copy( InputIt first, InputIt last,
 +
                                OutputIt d_first, const T& value );
 +
}}
 +
{{dcl rev end}}
 +
{{dcl rev begin|num=2}}
 +
{{dcl|since=c++17|until=c++26|
 +
template< class ExecutionPolicy,
 +
          class ForwardIt1, class ForwardIt2, class T >
 +
ForwardIt2 remove_copy( ExecutionPolicy&& policy,
 +
                        ForwardIt1 first, ForwardIt1 last,
 +
                        ForwardIt2 d_first, const T& value );
 
}}
 
}}
−
{{dcl | since=c++17 | until= | num=2 |1=
+
{{dcl|since=c++26|1=
−
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T >
+
template< class ExecutionPolicy,
−
ForwardIt2 remove_copy( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last,
+
          class ForwardIt1, class ForwardIt2,
 +
          class T = typename std::iterator_traits
 +
                        <ForwardIt1>::value_type >
 +
ForwardIt2 remove_copy( ExecutionPolicy&& policy,
 +
                        ForwardIt1 first, ForwardIt1 last,
 
                         ForwardIt2 d_first, const T& value );
 
                         ForwardIt2 d_first, const T& value );
 
}}
 
}}
−
{{dcl rev multi | num=3 | since1= | until1=c++20 |dcl1=
+
{{dcl rev end}}
−
template< class InputIt, class OutputIt, class UnaryPredicate >
+
{{dcla|num=3|notes={{mark constexpr since c++20}}|
−
OutputIt remove_copy_if( InputIt first, InputIt last, OutputIt d_first,
+
template< class InputIt, class OutputIt, class UnaryPred >
−
                         UnaryPredicate p );
+
OutputIt remove_copy_if( InputIt first, InputIt last,
−
|dcl2=
+
                         OutputIt d_first, UnaryPred p );
−
template< class InputIt, class OutputIt, class UnaryPredicate >
+
−
constexpr OutputIt remove_copy_if( InputIt first, InputIt last, OutputIt d_first,
+
−
                                  UnaryPredicate p );
+
 
}}
 
}}
−
{{dcl | since=c++17 | until= | num=4 |1=
+
{{dcl|num=4|since=c++17|
−
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class UnaryPredicate >
+
template< class ExecutionPolicy,
−
ForwardIt2 remove_copy_if( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last,
+
          class ForwardIt1, class ForwardIt2, class UnaryPred >
−
                           ForwardIt2 d_first, UnaryPredicate p );
+
ForwardIt2 remove_copy_if( ExecutionPolicy&& policy,
 +
                          ForwardIt1 first, ForwardIt1 last,
 +
                           ForwardIt2 d_first, UnaryPred p );
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
  
−
Copies elements from the range {{tt|[first, last)}}, to another range beginning at {{tt|d_first}}, omitting the elements which satisfy specific criteria. Source and destination ranges cannot overlap.
+
Copies elements from the range {{range|first|last}}, to another range beginning at {{c|d_first}}, omitting the elements which satisfy specific criteria.
  
−
@1@ Ignores all elements that are equal to {{tt|value}}.
+
@1@ Ignores all elements that are equal to {{c|value}} (using {{c/core|1=operator==}}).
−
@3@ Ignores all elements for which predicate {{tt|p}} returns {{c|true}}.
+
 
−
@2,4@ Same as {{v|1,3}}, but executed according to {{tt|policy}}. {{cpp/algorithm/parallel overload precondition|plural=true}}
+
@3@ Ignores all elements for which predicate {{c|p}} returns {{c|true}}.
 +
 
 +
@2,4@ Same as {{v|1,3}}, but executed according to {{c|policy}}.
 +
@@ {{cpp/algorithm/parallel overload precondition|plural=yes}}
 +
 
 +
If {{rev inl|until=c++20|{{c|1=*d_first = *first}} is invalid}}{{rev inl|since=c++20|{{c|*first}} is not [[cpp/iterator#Types and writability|writable]] to {{c|d_first}}}}, the program is ill-formed.
 +
 
 +
If source and destination ranges overlap, the behavior is undefined.
  
 
===Parameters===
 
===Parameters===
 
{{par begin}}
 
{{par begin}}
−
{{par | first, last | the range of elements to copy}}
+
{{par|first, last|the range of elements to copy}}
−
{{par | d_first | the beginning of the destination range. }}
+
{{par|d_first|the beginning of the destination range}}
−
{{par | value | the value of the elements not to copy}}
+
{{par|value|the value of the elements not to copy}}
 
{{par exec pol}}
 
{{par exec pol}}
 
{{par hreq}}
 
{{par hreq}}
−
{{par req named | InputIt | InputIterator}}
+
{{par req named|InputIt|InputIterator}}
−
{{par req named | OutputIt | OutputIterator}}
+
{{par req named|OutputIt|OutputIterator}}
−
{{par req named | ForwardIt1, ForwardIt2 | ForwardIterator}}
+
{{par req named|ForwardIt1, ForwardIt2|ForwardIterator}}
−
{{par req named | UnaryPredicate | Predicate}}
+
{{par req named|UnaryPred|Predicate}}
 
{{par end}}
 
{{par end}}
  
Line 56: Line 79:
  
 
===Complexity===
 
===Complexity===
−
Exactly {{c|std::distance(first, last)}} applications of the predicate.
+
Given {{mathjax-or|\(\scriptsize N\)|N}} as {{c|std::distance(first, last)}}:
 +
@1,2@ Exactly {{mathjax-or|\(\scriptsize N\)|N}} comparisons with {{c|value}} using {{c/core|1=operator==}}.
 +
@3,4@ Exactly {{mathjax-or|\(\scriptsize N\)|N}} applications of the predicate {{c|p}}.
  
−
For the overloads with an ExecutionPolicy, there may be a performance cost if {{tt|ForwardIt1}}'s value_type is not {{named req|MoveConstructible}}.
+
For the overloads with an ExecutionPolicy, there may be a performance cost if {{tt|ForwardIt1}}'s {{tt|value_type}} is not {{named req|MoveConstructible}}.
  
 
===Exceptions===
 
===Exceptions===
−
{{cpp/algorithm/parallel_exceptions_reporting_behavior|singular=no}}
+
{{cpp/algorithm/parallel exceptions reporting behavior|singular=no}}
  
 
===Possible implementation===
 
===Possible implementation===
−
{{eq fun | 1=
+
{{eq impl|title1=remove_copy (1)|ver1=1|1=
−
template<class InputIt, class OutputIt, class T>
+
template<class InputIt, class OutputIt,
−
OutputIt remove_copy(InputIt first, InputIt last,
+
        class T = typename std::iterator_traits<InputIt>::value_type>
−
                    OutputIt d_first, const T& value)
+
constexpr OutputIt remove_copy(InputIt first, InputIt last,
 +
                              OutputIt d_first, const T& value)
 
{
 
{
−
     for (; first != last; ++first) {
+
     for (; first != last; ++first)
−
         if (!(*first == value)) {
+
         if (!(*first == value))
 
             *d_first++ = *first;
 
             *d_first++ = *first;
−
        }
 
−
    }
 
 
     return d_first;
 
     return d_first;
 
}
 
}
−
| 2=
+
|title2=remove_copy_if (3)|ver2=3|2=
−
template<class InputIt, class OutputIt, class UnaryPredicate>
+
template<class InputIt, class OutputIt, class UnaryPred>
−
OutputIt remove_copy_if(InputIt first, InputIt last,
+
constexpr OutputIt remove_copy_if(InputIt first, InputIt last,
−
                        OutputIt d_first, UnaryPredicate p)
+
                                  OutputIt d_first, UnaryPred p)
 
{
 
{
−
     for (; first != last; ++first) {
+
     for (; first != last; ++first)
−
         if (!p(*first)) {
+
         if (!p(*first))
 
             *d_first++ = *first;
 
             *d_first++ = *first;
−
        }
 
−
    }
 
 
     return d_first;
 
     return d_first;
 
}
 
}
 
}}
 
}}
 +
 +
===Notes===
 +
{{feature test macro|__cpp_lib_algorithm_default_value_type|value=202403|std=C++26|[[cpp/language/list initialization|List-initialization]] for algorithms {{vl|1,2}}}}
  
 
===Example===
 
===Example===
 
{{example
 
{{example
−
| The following code outputs a string while erasing the hash characters '#' on the fly.
+
|code=
−
| code=
+
 
#include <algorithm>
 
#include <algorithm>
 +
#include <complex>
 +
#include <iomanip>
 +
#include <iostream>
 
#include <iterator>
 
#include <iterator>
 
#include <string>
 
#include <string>
−
#include <iostream>
+
#include <vector>
−
#include <iomanip>
+
 
 
int main()
 
int main()
 
{
 
{
 +
    // Erase the hash characters '#' on the fly.
 
     std::string str = "#Return #Value #Optimization";
 
     std::string str = "#Return #Value #Optimization";
−
     std::cout << "before: " << std::quoted(str) << "\n";
+
     std::cout << "before: " << std::quoted(str) << '\n';
  
 
     std::cout << "after:  \"";
 
     std::cout << "after:  \"";
Line 108: Line 136:
 
                     std::ostream_iterator<char>(std::cout), '#');
 
                     std::ostream_iterator<char>(std::cout), '#');
 
     std::cout << "\"\n";
 
     std::cout << "\"\n";
 +
 +
    // Erase {1, 3} value on the fly.
 +
    std::vector<std::complex<double>> nums{<!---->{2, 2}, {1, 3}, {4, 8}, {1, 3}<!---->};
 +
    std::remove_copy(nums.begin(), nums.end(),
 +
                    std::ostream_iterator<std::complex<double>>(std::cout),
 +
    #ifdef __cpp_lib_algorithm_default_value_type
 +
                    {1, 3}); // T gets deduced
 +
    #else
 +
                    std::complex<double>{1, 3});
 +
    #endif
 
}
 
}
−
| output=
+
|output=
 
before: "#Return #Value #Optimization"
 
before: "#Return #Value #Optimization"
 
after:  "Return Value Optimization"
 
after:  "Return Value Optimization"
 +
(2,2)(4,8)
 
}}
 
}}
 +
 +
===Defect reports===
 +
{{dr list begin}}
 +
{{dr list item|wg=lwg|dr=779|std=C++98|before={{tt|T}} was required to be {{named req|EqualityComparable}}, but<br>the value type of {{tt|ForwardIt}} is not always {{tt|T}}|after=required {{c|1=*d_first = *first}}<br>to be valid instead}}
 +
{{dr list end}}
  
 
===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/algorithm/dsc remove}}
+
{{dsc inc|cpp/algorithm/dsc remove}}
−
{{dsc inc | cpp/algorithm/dsc copy}}
+
{{dsc inc|cpp/algorithm/dsc copy}}
−
{{dsc inc | cpp/algorithm/dsc partition_copy}}
+
{{dsc inc|cpp/algorithm/dsc partition_copy}}
 +
{{dsc inc|cpp/algorithm/ranges/dsc remove_copy}}
 
{{dsc end}}
 
{{dsc end}}
  
 
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
 
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Latest revision as of 21:30, 20 May 2024

 
C++
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
remove_copyremove_copy_if
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
Defined in header <algorithm>
(1)
template< class InputIt, class OutputIt, class T >

OutputIt remove_copy( InputIt first, InputIt last,

                      OutputIt d_first, const T& value );
 (constexpr since C++20)
(until C++26)
template< class InputIt, class OutputIt,

          class T = typename std::iterator_traits
                        <InputIt>::value_type >
constexpr OutputIt remove_copy( InputIt first, InputIt last,

                                OutputIt d_first, const T& value );
 (since C++26)
(2)
template< class ExecutionPolicy,

          class ForwardIt1, class ForwardIt2, class T >
ForwardIt2 remove_copy( ExecutionPolicy&& policy,
                        ForwardIt1 first, ForwardIt1 last,

                        ForwardIt2 d_first, const T& value );
 (since C++17)
(until C++26)
template< class ExecutionPolicy,

          class ForwardIt1, class ForwardIt2,
          class T = typename std::iterator_traits
                        <ForwardIt1>::value_type >
ForwardIt2 remove_copy( ExecutionPolicy&& policy,
                        ForwardIt1 first, ForwardIt1 last,

                        ForwardIt2 d_first, const T& value );
 (since C++26)
template< class InputIt, class OutputIt, class UnaryPred >

OutputIt remove_copy_if( InputIt first, InputIt last,

                         OutputIt d_first, UnaryPred p );
 (3) (constexpr since C++20)
template< class ExecutionPolicy,

          class ForwardIt1, class ForwardIt2, class UnaryPred >
ForwardIt2 remove_copy_if( ExecutionPolicy&& policy,
                           ForwardIt1 first, ForwardIt1 last,

                           ForwardIt2 d_first, UnaryPred p );
 (4) (since C++17)

Copies elements from the range [first, last), to another range beginning at d_first, omitting the elements which satisfy specific criteria.

1) Ignores all elements that are equal to value (using operator==).
3) Ignores all elements for which predicate p returns true.
2,4) Same as (1,3), but executed according to policy.
These overloads participate in overload resolution only if

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

(until C++20)

std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.

(since C++20)

If *d_first = *first is invalid(until C++20)*first is not writable to d_first(since C++20), the program is ill-formed.

If source and destination ranges overlap, the behavior is undefined.

Contents

[edit] Parameters

first, last - the range of elements to copy
d_first - the beginning of the destination range
value - the value of the elements not to copy
policy - the execution policy to use. See execution policy for details.
Type requirements
-
InputIt must meet the requirements of LegacyInputIterator.
-
OutputIt must meet the requirements of LegacyOutputIterator.
-
ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.
-
UnaryPred must meet the requirements of Predicate.

[edit] Return value

Iterator to the element past the last element copied.

[edit] Complexity

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

1,2) Exactly N comparisons with value using operator==.
3,4) Exactly N applications of the predicate p.

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

[edit] 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.

[edit] Possible implementation

remove_copy (1) 
template<class InputIt, class OutputIt,
         class T = typename std::iterator_traits<InputIt>::value_type>
constexpr OutputIt remove_copy(InputIt first, InputIt last,
                               OutputIt d_first, const T& value)
{
    for (; first != last; ++first)
        if (!(*first == value))
            *d_first++ = *first;
    return d_first;
}
remove_copy_if (3) 
template<class InputIt, class OutputIt, class UnaryPred>
constexpr OutputIt remove_copy_if(InputIt first, InputIt last,
                                  OutputIt d_first, UnaryPred p)
{
    for (; first != last; ++first)
        if (!p(*first))
            *d_first++ = *first;
    return d_first;
}

[edit] Notes

Feature-test macro Value Std Feature
__cpp_lib_algorithm_default_value_type 202403 (C++26) List-initialization for algorithms (1,2)

[edit] Example

Run this code
#include <algorithm>
#include <complex>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
 
int main()
{
    // Erase the hash characters '#' on the fly.
    std::string str = "#Return #Value #Optimization";
    std::cout << "before: " << std::quoted(str) << '\n';
 
    std::cout << "after:  \"";
    std::remove_copy(str.begin(), str.end(),
                     std::ostream_iterator<char>(std::cout), '#');
    std::cout << "\"\n";
 
    // Erase {1, 3} value on the fly.
    std::vector<std::complex<double>> nums{{2, 2}, {1, 3}, {4, 8}, {1, 3}};
    std::remove_copy(nums.begin(), nums.end(),
                     std::ostream_iterator<std::complex<double>>(std::cout),
    #ifdef __cpp_lib_algorithm_default_value_type
                     {1, 3}); // T gets deduced
    #else
                     std::complex<double>{1, 3});
    #endif
}

Output: 

before: "#Return #Value #Optimization"
after:  "Return Value Optimization"
(2,2)(4,8)

[edit] Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 779 C++98 T was required to be EqualityComparable, but
the value type of ForwardIt is not always T 		required *d_first = *first
to be valid instead

[edit] See also

 removes elements satisfying specific criteria
(function template) [edit]
(C++11)
 copies a range of elements to a new location
(function template) [edit]
(C++11)
 copies a range dividing the elements into two groups
(function template) [edit]
(C++20)(C++20)
 copies a range of elements omitting those that satisfy specific criteria
(niebloid)[edit]
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/algorithm/remove_copy&oldid=171924"