Namespaces
Variants
Views
Actions

std::replace_copy, std::replace_copy_if

From cppreference.com
< cpp‎ | algorithm
 
 
Algorithm library
Execution policies (C++17)
Non-modifying sequence operations
(C++11)(C++11)(C++11)
(C++17)
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
(C++11)
Binary search operations
Set operations (on sorted ranges)
Heap operations
(C++11)
Minimum/maximum operations
(C++11)
(C++17)
Permutations
Numeric operations
C library
 
Defined in header <algorithm>
(1)
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 );
(until C++20)
template< class InputIt, class OutputIt, class T >

constexpr OutputIt replace_copy( InputIt first, InputIt last, OutputIt d_first,

                                 const T& old_value, const T& new_value );
(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T >

ForwardIt2 replace_copy( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last,

                         ForwardIt2 d_first, const T& old_value, const T& new_value );
(2) (since C++17)
(3)
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 );
(until C++20)
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 );
(since C++20)
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 );
(4) (since C++17)

Copies the all 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

Contents

[edit] 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.
p - unary predicate which returns ​true if the element value 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 (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.

[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 and ExecutionPolicy is one of the three 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

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;
}

[edit] Example

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

#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

[edit] See also

removes elements satisfying specific criteria
(function template) [edit]