std::ranges::replace, std::ranges::replace_if
From cppreference.com
| Defined in header <algorithm>
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| Call signature |
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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 = {} );
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(1) | (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 = std::iter_value_t<I> >
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 = {} );
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(since C++26) | |
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 = {} );
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(2) | (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 = ranges::range_value_t<R> >
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 = {} );
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(since C++26) | |
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 = {} );
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(3) | (since C++20) (until C++26) |
template< std::input_iterator I, std::sentinel_for<I> S,
class Proj = std::identity, class T = std::iter_value_t<I>,
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 = {} );
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(since C++26) | |
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 = {} );
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(4) | (since C++20) (until C++26) |
template< ranges::input_range R, class Proj = std::identity,
class T = ranges::range_value_t<R>,
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 = {} );
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(since C++26) | |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_sentinel_for<I> S,
class Proj = std::identity,
class T1 = std::projected_value_t<I, Proj>,
class T2 = std::iter_value_t<I> >
requires std::indirectly_writable<I, const T2&> &&
std::indirect_binary_predicate
<ranges::equal_to, std::projected<I, Proj>, const T1*>
I replace( Ep&& policy, I first, S last, const T1& old_value,
const T2& new_value, Proj proj = {} );
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(5) | (since C++26) |
template< /*execution-policy*/ Ep,
/*sized-random-access-range*/ R, class Proj = std::identity,
class T1 = std::projected_value_t<ranges::iterator_t<R>, Proj>,
class T2 = ranges::range_value_t<R> >
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*>
ranges::borrowed_iterator_t<R>
replace( Ep&& policy, R&& r, const T1& old_value,
const T2& new_value, Proj proj = {} );
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(6) | (since C++26) |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_sentinel_for<I> S,
class Proj = std::identity, class T = std::iter_value_t<I>,
std::indirect_unary_predicate<std::projected<I, Proj>> Pred>
requires std::indirectly_writable<I, const T&>
I replace_if( Ep&& policy, I first, S last, Pred pred,
const T& new_value, Proj proj = {} );
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(7) | (since C++26) |
template< /*execution-policy*/ Ep,
/*sized-random-access-range*/ R, class Proj = std::identity,
class T = ranges::range_value_t<R>,
std::indirect_unary_predicate
<std::projected<ranges::iterator_t<R>, Proj>> Pred>
requires std::indirectly_writable<ranges::iterator_t<R>, const T&>
ranges::borrowed_iterator_t<R>
replace_if( Ep&& policy, R&& r, Pred pred,
const T& new_value, Proj proj = {} );
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(8) | (since C++26) |
For the definition of /*execution-policy*/, see this page; for the definition of /*sized-random-access-range*/, see this page.
Replaces the elements (projected by proj) in the target range [first, last) or r with new_value if they satisfy specific criteria.
1,2)
replace replaces all elements that are equal to old_value (using operator==).3,4)
replace_if replaces all elements for which predicate pred returns true.5-8) Same as (1-4), but executed according to
policy.If new_value is not writable to first, the program is ill-formed.
The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:
- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
Parameters
| first, last | - | the iterator-sentinel pair defining the target range |
| r | - | the target range |
| old_value | - | the value of elements to replace |
| new_value | - | the value to use as a replacement |
| pred | - | predicate to be applied to the projected elements |
| proj | - | the projection to be applied to the elements |
| policy | - | the execution policy to use |
Return value
The past-the-end iterator of the target range.
Complexity
Given N as ranges::distance(first, last) or ranges::distance(r):
1,2) Exactly N comparisons using
operator==, and exactly N applications of proj.3,4) Exactly N applications of
pred and proj.5,6) 𝓞(N) comparisons using
operator==, and 𝓞(N) applications of proj.7,8) 𝓞(N) applications of
pred and proj.Exceptions
5-8) During the execution process:
- If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
- If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).
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 target range.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_algorithm_default_value_type |
202403 |
(C++26) | List-initialization for algorithms (1-4) |
Possible implementation
| replace |
|---|
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::next(r),
old_value, new_value, std::move(proj));
}
template<ranges::forward_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::next(ranges::begin(r), ranges::end(r)),
old_value, new_value, std::move(proj));
}
};
inline constexpr replace_fn replace{};
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| replace_if |
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));
}
template<ranges::forward_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::next(ranges::begin(r), ranges::end(r)),
std::move(pred), new_value, std::move(proj));
}
};
inline constexpr replace_if_fn replace_if{};
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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)
See also
| replaces all values satisfying specific criteria with another value (function template) | |
(C++20)(C++20) |
copies a range, replacing elements satisfying specific criteria with another value (algorithm function object) |