std::remove_copy, std::remove_copy_if

Defined in header `<algorithm>`
template< class InputIt, class OutputIt, class T > OutputIt remove_copy( InputIt first, InputIt last, OutputIt d_first, const T& value );	(1)
template< class ExecutionPolicy, class InputIt, class OutputIt, class T > OutputIt remove_copy( ExecutionPolicy&& policy, InputIt first, InputIt last, OutputIt d_first, const T& value );	(2)	(since C++17)
template< class InputIt, class OutputIt, class UnaryPredicate > OutputIt remove_copy_if( InputIt first, InputIt last, OutputIt d_first, UnaryPredicate p );	(3)
template< class ExecutionPolicy, class InputIt, class OutputIt, class UnaryPredicate > OutputIt remove_copy_if( ExecutionPolicy&& policy, InputIt first, InputIt last, OutputIt d_first, UnaryPredicate 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. Source and destination ranges cannot overlap.

1) Ignores all elements that are equal to value.

3) Ignores all elements for which predicate p returns true.

2,4) Same as (1,3), but executed according to policy. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

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 `InputIterator`.
- `OutputIt` must meet the requirements of `OutputIterator`.
- `UnaryPredicate` must meet the requirements of `Predicate`.

[edit] Return value

Iterator to the element past the last element copied.

[edit] Complexity

Exactly last - first applications of the predicate.

[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,

if policy is std::parallel_vector_execution_policy, std::terminate is called
if policy is std::sequential_execution_policy or std::parallel_execution_policy, the algorithm exits with an std::exception_list containing all uncaught exceptions. If there was only one uncaught exception, the algorithm may rethrow it without wrapping in std::exception_list. It is unspecified how much work the algorithm will perform before returning after the first exception was encountered.
if policy is some other type, the behavior is implementation-defined

If the algorithm fails to allocate memory (either for itself or to construct an std::exception_list when handling a user exception), std::bad_alloc is thrown.

[edit] Possible implementation

First version

template<class InputIt, class OutputIt, class T>
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;
}

Second version

template<class InputIt, class OutputIt, class UnaryPredicate>
OutputIt remove_copy_if(InputIt first, InputIt last,
                        OutputIt d_first, UnaryPredicate p)
{
    for (; first != last; ++first) {
        if (!p(*first)) {
            *d_first++ = *first;
        }
    }
    return d_first;
}

[edit] Example

The following code outputs a string while erasing the spaces on the fly.

Run this code

#include <algorithm>
#include <iterator>
#include <string>
#include <iostream>
int main()
{
    std::string str = "Text with some   spaces";
    std::cout << "before: " << str << "\n";
 
    std::cout << "after:  ";
    std::remove_copy(str.begin(), str.end(),
                     std::ostream_iterator<char>(std::cout), ' ');
    std::cout << '\n';
}

Output:

before: Text with some   spaces
after:  Textwithsomespaces

[edit] See also

removeremove_if	removes elements satisfying specific criteria (function template)
copycopy_if (C++11)	copies a range of elements to a new location (function template)
std::experimental::parallel::remove_copy (parallelism TS)	parallelized version of `std::remove_copy` (function template)
std::experimental::parallel::remove_copy_if (parallelism TS)	parallelized version of `std::remove_copy_if` (function template)

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications