Std::replace,std::replace_if (3) Linux Manual Page

std::replace,std::replace_if – std::replace,std::replace_if

Synopsis

Defined in header<algorithm>

    template <class ForwardIt, class T>

    void replace(ForwardIt first, ForwardIt last, (until C++ 20)

                                                      const T &old_value,
                 const T &new_value);

template <class ForwardIt, class T>

constexpr void replace(ForwardIt first, ForwardIt last, (since C++ 20)

                                                            const T &old_value,
                       const T &new_value);

template <class ExecutionPolicy, class ForwardIt, class T>

void replace(ExecutionPolicy &&policy, ForwardIt first, ForwardIt last, (2)(since C++ 17)

                                                                            const T &old_value,
             const T &new_value);
(1)

    template <class ForwardIt, class UnaryPredicate, class T>

    void replace_if(ForwardIt first, ForwardIt last, (until C++ 20)

                                                         UnaryPredicate p,
                    const T &new_value);

template <class ForwardIt, class UnaryPredicate, class T>

constexpr void replace_if(ForwardIt first, ForwardIt last, (3)(since C++ 20)

                                                               UnaryPredicate p,
                          const T &new_value);

template <class ExecutionPolicy, class ForwardIt, class UnaryPredicate, class T>

void replace_if(ExecutionPolicy &&policy, ForwardIt first, ForwardIt last, (4)(since C++ 17)

                                                                               UnaryPredicate p,
                const T &new_value);

Replaces all elements satisfying specific criteria with new_value in the range [first, last).
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. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

Parameters

first, last – the range of elements to process
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 ForwardIt, 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

–
ForwardIt must meet the requirements of LegacyForwardIterator.
–
UnaryPredicate must meet the requirements of Predicate.

Return value

(none)

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.

Notes

Because the algorithm takes old_value and new_value by reference, it can have unexpected behavior if either is a reference to an element of the range [first, last).

Possible implementation

First version

  template<class ForwardIt, class T>
  void replace(ForwardIt first, ForwardIt last,
               const T& old_value, const T& new_value)
  {
      for (; first != last; ++first) {
          if (*first == old_value) {
              *first = new_value;
          }
      }
  }

Second version

  template<class ForwardIt, class UnaryPredicate, class T>
  void replace_if(ForwardIt first, ForwardIt last,
                  UnaryPredicate p, const T& new_value)
  {
      for (; first != last; ++first) {
          if(p(*first)) {
              *first = new_value;
          }
      }
  }

Example

The following code at first replaces all occurrences of 8 with 88 in a vector of integers. Then it replaces all values less than 5 with 55.
// Run this code

#include <algorithm>

#include <array>

#include <iostream>

#include <functional>
int main()

{
    std::array<int, 10> s{5, 7, 4, 2, 8, 6, 1, 9, 0, 3};
    std::replace(s.begin(), s.end(), 8, 88);
    for (int a : s) {
        std::cout << a << " ";
    }
    std::cout << '\n';
    std::replace_if(s.begin(), s.end(),
                    std::bind(std::less<int>(), std::placeholders::_1, 5), 55);
    for (int a : s) {
        std::cout << a << " ";
    }
    std::cout << '\n';
}

Output:

5 7 4 2 88 6 1 9 0 3
5 7 55 55 88 6 55 9 55 55

std::replace,std::replace_if (3) Linux Manual Page