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std::ranges::replace, std::ranges::replace_if

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
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(C++17)
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(C++11)                (C++11)(C++11)

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(C++11)
(C++11)
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(until C++17)(C++11)
(C++20)(C++20)
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(C++17)

Sorting and related operations
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(on partitioned ranges) Set operations (on sorted ranges) Merge operations (on sorted ranges) Heap operations
(C++11)
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C library
Numeric operations
 
Constrained algorithms
All names in this menu belong to namespace std::ranges
Non-modifying sequence operations
Modifying sequence operations
replacereplace_if
Partitioning operations
Sorting operations
       
Binary search operations (on sorted ranges)
       
       
    
Set operations (on sorted ranges)
     
        
Heap operations
     
         
Minimum/maximum operations
       
       
Permutation operations
Fold operations
(C++23)
(C++23)  
(C++23)
(C++23)  
Defined in header <algorithm>
Call signature
(1)
template< std::input_iterator I, std::sentinel_for <I> S,

          class T1, class T2, class Proj = std::identity >
requires std::indirectly_writable <I, const T2&> &&
         std::indirect_binary_predicate
             <ranges::equal_to, std::projected <I, Proj>, const T1*>
constexpr I replace( I first, S last, const T1& old_value,

                     const T2& new_value, Proj proj = {} );
(since C++20)
(until C++26)
template< std::input_iterator I, std::sentinel_for <I> S,

          class Proj = std::identity,
          class T1 = std::projected_value_t<I, Proj>, class T2 = T1 >
requires std::indirectly_writable <I, const T2&> &&
         std::indirect_binary_predicate
             <ranges::equal_to, std::projected <I, Proj>, const T1*>
constexpr I replace( I first, S last, const T1& old_value,

                     const T2& new_value, Proj proj = {} );
(since C++26)
(2)
template< ranges::input_range R,

          class T1, class T2, class Proj = std::identity >
requires std::indirectly_writable <ranges::iterator_t <R>, const T2&> &&
         std::indirect_binary_predicate
             <ranges::equal_to,
              std::projected <ranges::iterator_t <R>, Proj>, const T1*>
constexpr ranges::borrowed_iterator_t <R>
    replace( R&& r, const T1& old_value,

             const T2& new_value, Proj proj = {} );
(since C++20)
(until C++26)
template< ranges::input_range R,

          class Proj = std::identity,
          class T1 = std::projected_value_t<ranges::iterator_t <R>, Proj>,
          class T2 = T1 >
requires std::indirectly_writable <ranges::iterator_t <R>, const T2&> &&
         std::indirect_binary_predicate
             <ranges::equal_to,
              std::projected <ranges::iterator_t <R>, Proj>, const T1*>
constexpr ranges::borrowed_iterator_t <R>
    replace( R&& r, const T1& old_value,

             const T2& new_value, Proj proj = {} );
(since C++26)
(3)
template< std::input_iterator I, std::sentinel_for <I> S,

          class T, class Proj = std::identity,
          std::indirect_unary_predicate <std::projected <I, Proj>> Pred >
requires std::indirectly_writable <I, const T&>
constexpr I replace_if( I first, S last, Pred pred,

                        const T& new_value, Proj proj = {} );
(since C++20)
(until C++26)
template< std::input_iterator I, std::sentinel_for <I> S,

          class Proj = std::identity,
          class T = std::projected_value_t<I, Proj>,
          std::indirect_unary_predicate <std::projected <I, Proj>> Pred >
requires std::indirectly_writable <I, const T&>
constexpr I replace_if( I first, S last, Pred pred,

                        const T& new_value, Proj proj = {} );
(since C++26)
(4)
template< ranges::input_range R, class T, class Proj = std::identity,

          std::indirect_unary_predicate <
              std::projected <ranges::iterator_t <R>, Proj>> Pred >
requires std::indirectly_writable <ranges::iterator_t <R>, const T&>
constexpr ranges::borrowed_iterator_t <R>

    replace_if( R&& r, Pred pred, const T& new_value, Proj proj = {} );
(since C++20)
(until C++26)
template< ranges::input_range R, class Proj = std::identity,

          class T = std::projected_value_t<ranges::iterator_t <R>, Proj>,
          std::indirect_unary_predicate <
              std::projected <ranges::iterator_t <R>, Proj>> Pred >
requires std::indirectly_writable <ranges::iterator_t <R>, const T&>
constexpr ranges::borrowed_iterator_t <R>

    replace_if( R&& r, Pred pred, const T& new_value, Proj proj = {} );
(since C++26)

Replaces all elements satisfying specific criteria with new_value in the range [first, last).

1) Replaces all elements that are equal to old_value, using std::invoke (proj, *i) == old_value to compare.
3) Replaces all elements for which the predicate pred evaluates to true, where evaluating expression is std::invoke (pred, std::invoke (proj, *i)).
2,4) Same as (1,3), but uses r as the range, as if using ranges::begin (r) as first and ranges::end (r) as last.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

Contents

[edit] Parameters

first, last - the iterator-sentinel pair defining the range of elements to process
r - the range of elements to process
old_value - the value of elements to replace
new_value - the value to use as a replacement
pred - predicate to apply to the projected elements
proj - projection to apply to the elements

[edit] Return value

An iterator equal to last.

[edit] Complexity

Exactly ranges::distance (first, last) applications of the corresponding predicate comp and any projection proj.

[edit] Notes

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

Feature-test macro Value Std Feature
__cpp_lib_algorithm_default_value_type 202403 (C++26) List-initialization for algorithms (1-4)

[edit] Possible implementation

replace (1,2) 
struct replace_fn
{
 template<std::input_iterator I, std::sentinel_for <I> S, class Proj = std::identity,
 class T1 = std::projected_value_t<I, Proj>, class T2 = T1>
 requires std::indirectly_writable <I, const T2&> && 
 std::indirect_binary_predicate
 <ranges::equal_to, std::projected <I, Proj>, const T1*>
 constexpr I operator()(I first, S last, const T1& old_value,
 const T2& new_value, Proj proj = {}) const
 {
 for (; first != last; ++first)
 if (old_value == std::invoke (proj, *first))
 *first = new_value;
 return first;
 }
 
 template<ranges::input_range R, class Proj = std::identity
 class T1 = std::projected_value_t<ranges::iterator_t <R>, Proj>,
 class T2 = T1>
 requires std::indirectly_writable <ranges::iterator_t <R>, const T2&> &&
 std::indirect_binary_predicate <ranges::equal_to,
 std::projected <ranges::iterator_t <R>, Proj>, const T1*>
 constexpr ranges::borrowed_iterator_t <R>
 operator()(R&& r, const T1& old_value,
 const T2& new_value, Proj proj = {}) const
 {
 return (*this)(ranges::begin (r), ranges::end (r), old_value,
 new_value, std::move(proj));
 }
};
 
inline constexpr replace_fn replace{};
replace_if (3,4) 
struct replace_if_fn
{
 template<std::input_iterator I, std::sentinel_for <I> S,
 class Proj = std::identity, class T = std::projected_value_t<I, Proj>,
 std::indirect_unary_predicate <std::projected <I, Proj>> Pred>
 requires std::indirectly_writable <I, const T&>
 constexpr I operator()(I first, S last, Pred pred,
 const T& new_value, Proj proj = {}) const
 {
 for (; first != last; ++first)
 if (!!std::invoke (pred, std::invoke (proj, *first)))
 *first = new_value;
 return std::move(first);
 }
 
 template<ranges::input_range R, class Proj = std::identity,
 class T = std::projected_value_t<ranges::iterator_t <R>, Proj>
 std::indirect_unary_predicate
 <std::projected <ranges::iterator_t <R>, Proj>> Pred>
 requires std::indirectly_writable <ranges::iterator_t <R>, const T&>
 constexpr ranges::borrowed_iterator_t <R>
 operator()(R&& r, Pred pred, const T& new_value, Proj proj = {}) const
 {
 return (*this)(ranges::begin (r), ranges::end (r), std::move(pred),
 new_value, std::move(proj));
 }
};
 
inline constexpr replace_if_fn replace_if{};

[edit] Example

Run this code
#include <algorithm>
#include <array>
#include <complex>
#include <iostream>
 
void println(const auto& v)
{
 for (const auto& e : v)
 std::cout << e << ' ';
 std::cout << '\n';
}
 
int main()
{
 namespace ranges = std::ranges;
 
 std::array p{1, 6, 1, 6, 1, 6};
 println(p);
 ranges::replace(p, 6, 9);
 println(p);
 
 std::array q{1, 2, 3, 6, 7, 8, 4, 5};
 println(q);
 ranges::replace_if(q, [](int x) { return 5 < x; }, 5);
 println(q);
 
 std::array <std::complex <double>, 2> nums{{{1, 3}, {1, 3}}};
 println(nums);
 #ifdef __cpp_lib_algorithm_default_value_type
 ranges::replace(nums, {1, 3}, {4, 2});
 #else
 ranges::replace(nums, std::complex <double>{1, 3}, std::complex <double>{4, 2});
 #endif
 println(nums);
}

Output: 

1 6 1 6 1 6
1 9 1 9 1 9
1 2 3 6 7 8 4 5
1 2 3 5 5 5 4 5
(1,3) (1,3)
(4,2) (4,2)

[edit] See also

copies a range, replacing elements satisfying specific criteria with another value
(algorithm function object)[edit]
replaces all values satisfying specific criteria with another value
(function template) [edit]

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