std::replace_copy,std::replace_copy_if (3) - Linux Manuals

std::replace_copy,std::replace_copy_if: std::replace_copy,std::replace_copy_if

NAME

std::replace_copy,std::replace_copy_if - std::replace_copy,std::replace_copy_if

Synopsis

Defined in header <algorithm>
template< class InputIt, class OutputIt, class T >
OutputIt replace_copy( InputIt first, InputIt last, OutputIt d_first, (until C++20)
const T& old_value, const T& new_value );
template< class InputIt, class OutputIt, class T >
constexpr OutputIt replace_copy( InputIt first, InputIt last, OutputIt d_first, (since C++20)
const T& old_value, const T& new_value );
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T >
ForwardIt2 replace_copy( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, (2) (since C++17)
ForwardIt2 d_first, const T& old_value, const T& new_value ); (1)
template< class InputIt, class OutputIt, class UnaryPredicate, class T >
OutputIt replace_copy_if( InputIt first, InputIt last, OutputIt d_first, (until C++20)
UnaryPredicate p, const T& new_value );
template< class InputIt, class OutputIt, class UnaryPredicate, class T >
constexpr OutputIt replace_copy_if( InputIt first, InputIt last, OutputIt d_first, (3) (since C++20)
UnaryPredicate p, const T& new_value );
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class UnaryPredicate, class T >
ForwardIt2 replace_copy_if( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, (4) (since C++17)
ForwardIt2 d_first, UnaryPredicate p, const T& new_value );

Copies the elements from the range [first, last) to another range beginning at d_first replacing all elements satisfying specific criteria with new_value. The source and destination ranges cannot overlap.
1) Replaces all elements that are equal to old_value.
3) Replaces all elements for which predicate p returns true.
2,4) Same as (1,3), but executed according to policy. This overload only participates in overload resolution if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

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
policy - the execution policy to use. See execution_policy for details.
              unary predicate which returns true if the element value should be replaced.
p - 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
              (since C++11).
new_value - the value to use as replacement

Type requirements

-
InputIt must meet the requirements of LegacyInputIterator.
-
OutputIt must meet the requirements of LegacyOutputIterator.
-
ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.

Return value

Iterator to the element past the last element copied.

Complexity

Exactly last - first applications of the predicate.

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

First version

  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;
  }

Second version

  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;
  }

Example

The following copy prints a vector, replacing all values over 5 with 99 on the fly.
// Run this code

  #include <algorithm>
  #include <vector>
  #include <iostream>
  #include <iterator>
  #include <functional>

  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