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 = |
(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.
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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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.
Complexity
At most two comparisons and three applications of the projection.
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; |
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.
Example
#include <algorithm> #include <cstdint> #include <iostream> #include <iomanip> #include <string> using namespace std::literals; namespace ranges = std::ranges; 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) << ranges::clamp(v, INT8_MIN, INT8_MAX) << std::setw(21) << 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) << ranges::clamp(v, "-128"s, "127"s, {}, stoi) << std::setw(21) << 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
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) |