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 );
   If the value of v is within [lo, hi], returns v; otherwise returns the nearest
   boundary.
   1) Uses
   operator<
   (until C++20)
   std::less{}
   (since C++20) to compare the values.
   If T is not LessThanComparable, the behavior is undefined.^[1]
   2) Uses the comparison function comp to compare the values.
   If lo is greater than hi, the behavior is undefined.
    1. ↑ If NaN is avoided, T can be a floating-point type.

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.

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
   1) At most two comparisons using
   operator<
   (until C++20)
   std::less{}
   (since C++20).
   2) At most two applications of the comparison function comp.

Possible implementation
                        clamp (1)
   template<class T>
   constexpr const T& clamp(const T& v, const T& lo, const T& hi)
   {
       return clamp(v, lo, hi, less{});
   }
                        clamp (2)
   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 Value Std Feature
   __cpp_lib_clamp 201603L (C++17) std::clamp

Example
// Run this code
 #include <algorithm>
 #include <cstdint>
 #include <iomanip>
 #include <iostream>
 int main()
 {
     std::cout << "[raw] "
                  "[" << INT8_MIN << ',' << INT8_MAX << "] "
                  "[0," << UINT8_MAX << "]\n";
     for (const int v : {-129, -128, -1, 0, 42, 127, 128, 255, 256})
         std::cout << std::setw(4) << v
                   << std::setw(11) << std::clamp(v, INT8_MIN, INT8_MAX)
                   << std::setw(8) << std::clamp(v, 0, UINT8_MAX) << '\n';
 }

Output:
 [raw] [-128,127] [0,255]
 -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
   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)