std::clamp(3)

NAME
std::clamp - std::clamp

Synopsis
   Defined in header <algorithm>
   template<class T> (1) (since C++17)
   constexpr const T& clamp( const T& v, const T& lo, const T& hi );
   template<class T, class Compare>
   constexpr const T& clamp( const T& v, const T& lo, const T& hi, (2) (since C++17)
   Compare comp );
   1) If v compares less than lo, returns lo; otherwise if hi compares less than v,
   returns hi; otherwise returns v.
   Uses operator< to compare the values.
   2) Same as (1), but uses comp to compare the values.
   The behavior is undefined if the value of lo is greater than hi.

Parameters
   v - the value to clamp
   lo,hi - the boundaries to clamp v to
           comparison function object (i.e. an object that satisfies the requirements
           of Compare) which returns true if the first argument is less than the
           second.
           The signature of the comparison function should be equivalent to the
           following:
           bool cmp(const Type1 &a, const Type2 &b);
   comp -
           While the signature does not need to have const &, the function must not
           modify the objects passed to it and must be able to accept all values of
           type (possibly const) Type1 and Type2 regardless of value category (thus,
           Type1 & is not allowed
           , nor is Type1 unless for Type1 a move is equivalent to a copy
           (since C++11)).
           The types Type1 and Type2 must be such that an object of type T can be
           implicitly converted to both of them.

Type requirements
   -
   T must meet the requirements of LessThanComparable in order to use overloads (1).
   However, if NaN is avoided, T can be a floating-point type.

Return value
   Reference to lo if v is less than lo, reference to hi if hi is less than v,
   otherwise reference to v.

Complexity
   At most two comparisons.

Possible implementation

First version
   template<class T>
   constexpr const T& clamp( const T& v, const T& lo, const T& hi )
   {
       return clamp(v, lo, hi, less{});
   }

Second version
   template<class T, class Compare>
   constexpr const T& clamp( const T& v, const T& lo, const T& hi, Compare comp )
   {
       return comp(v, lo) ? lo : comp(hi, v) ? hi : v;
   }

Notes
   Capturing the result of std::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::clamp(n, 0, 255);
 // r is dangling
   If v compares equivalent to either bound, returns a reference to v, not the bound.
   Feature-test macro: __cpp_lib_clamp

Example
// Run this code
 #include <cstdint>
 #include <algorithm>
 #include <iostream>
 #include <iomanip>
 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::clamp(v, INT8_MIN, INT8_MAX)
                   << std::setw(21) << std::clamp(v, 0, UINT8_MAX) << '\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

See also
   min returns the smaller of the given values
                 (function template)
   max returns the greater of the given values
                 (function template)
   in_range checks if an integer value is in the range of a given integer type
   (C++20) (function template)
   ranges::clamp clamps a value between a pair of boundary values
   (C++20) (niebloid)