std::replace() algorithm

since C++20

// (1)
template< class ForwardIt, class T >
constexpr void replace( ForwardIt first, ForwardIt last,
                        const T& old_value, const T& new_value );

// (2)
template< class ExecutionPolicy, class ForwardIt, class T >
void replace( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last,
              const T& old_value, const T& new_value );

since C++17

// (1)
template< class ForwardIt, class T >
void replace( ForwardIt first, ForwardIt last,
              const T& old_value, const T& new_value );

// (2)
template< class ExecutionPolicy, class ForwardIt, class T >
void replace( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last,
              const T& old_value, const T& new_value );

until C++17

// (1)
template< class ForwardIt, class T >
void replace( ForwardIt first, ForwardIt last,
              const T& old_value, const T& new_value );

• (1) Replaces all elements equal to old_value with new_value in the range [first; last).

• (2) Same as (1), but executed according to policy.

  Overload Resolution

  These overloads participate in overload resolution only if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>  (until C++20) std::is_execution_policy_v<std::replace_cvref_t<ExecutionPolicy>>  (since C++20) is true.

Parameters

first last	The range of elements to process.
old_value	The value to search for and replace.
new_value	The value to use as a replacement.
policy	The execution policy to use. See execution policy for details.

Type requirements

ForwardIt

LegacyForwardIterator

since C++20

*first

Must be writable to d_first.

until C++20

The expression *first = new_value must be valid.

Return value

(none)

Complexity

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

At most N comparisons with old_value using operator==.

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

replace (1)

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;
}

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).

Examples

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).

Main.cpp

#include <algorithm>
#include <array>
#include <functional>
#include <iostream>

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