std::ranges::clamp
| Defined in header <algorithm>
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| Call signature |
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| template< class T, class Proj = std::identity, std::indirect_strict_weak_order<std::projected<const T*, Proj>> Comp = ranges::less > |
(since C++20) | |
If v compares less than lo, returns lo; otherwise if hi compares less than v, returns hi; otherwise returns v.
The behavior is undefined if lo is greater than hi.
The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists may not be specified when calling any of them.
- None of them is visible to argument-dependent lookup.
- When one of them is found by normal unqualified lookup for the name to the left of the function-call operator, it inhibits argument-dependent lookup.
In practice, they may be implemented as function objects, or with special compiler extensions.
Contents |
[edit] Parameters
| v | - | the value to clamp |
| lo, hi | - | the boundaries to clamp v to
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| comp | - | the comparison to apply to the projected elements |
| proj | - | the projection to apply to v, lo and hi
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[edit] Return value
Reference to lo if the projected value of v is less than the projected value of lo, reference to hi if the projected value of hi is less than the projected value of v, otherwise reference to v.
[edit] Complexity
At most two comparisons and three applications of the projection.
[edit] Possible implementation
struct clamp_fn { template<class T, class Proj = std::identity, std::indirect_strict_weak_order<std::projected<const T*, Proj>> Comp = ranges::less> constexpr const T& operator()(const T& v, const T& lo, const T& hi, Comp comp = {}, Proj proj = {}) const { auto&& pv = std::invoke(proj, v); return std::invoke(comp, std::forward<decltype(pv)>(pv), std::invoke(proj, lo)) ? lo : std::invoke(comp, std::invoke(proj, hi), std::forward<decltype(pv)>(pv)) ? hi : v; } }; inline constexpr clamp_fn clamp; |
[edit] Notes
std::ranges::clamp by reference produces a dangling reference if one of the parameters is a temporary and that parameter is returned:
int n = 1; const int& r = std::ranges::clamp(n-1, n+1); // r is dangling
If v compares equivalent to either bound, returns a reference to v, not the bound.
[edit] Example
#include <algorithm> #include <cstdint> #include <iostream> #include <iomanip> #include <string> using namespace std::literals; int main() { std::cout << " raw clamped to int8_t clamped to uint8_t\n"; for(int const v: {-129, -128, -1, 0, 42, 127, 128, 255, 256}) { std::cout << std::setw(04) << v << std::setw(20) << std::ranges::clamp(v, INT8_MIN, INT8_MAX) << std::setw(21) << std::ranges::clamp(v, 0, UINT8_MAX) << '\n'; } std::cout << '\n'; // Projection function const auto stoi = [](std::string s) { return std::stoi(s); }; // Same as above, but with strings for(std::string const v: {"-129", "-128", "-1", "0", "42", "127", "128", "255", "256"}) { std::cout << std::setw(04) << v << std::setw(20) << std::ranges::clamp(v, "-128"s, "127"s, {}, stoi) << std::setw(21) << std::ranges::clamp(v, "0"s, "255"s, {}, stoi) << '\n'; } }
Output:
raw clamped to int8_t clamped to uint8_t -129 -128 0 -128 -128 0 -1 -1 0 0 0 0 42 42 42 127 127 127 128 127 128 255 127 255 256 127 255 -129 -128 0 -128 -128 0 -1 -1 0 0 0 0 42 42 42 127 127 127 128 127 128 255 127 255 256 127 255
[edit] See also
| (C++20) |
returns the smaller of the given values (niebloid) |
| (C++20) |
returns the greater of the given values (niebloid) |
| (C++20) |
checks if an integer value is in the range of a given integer type (function template) |
| (C++17) |
clamps a value between a pair of boundary values (function template) |
