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    std::clamp

    From cppreference.com
     
    C++
     
    Algorithm library
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    Defined in header <algorithm> 
    template< class T >
constexpr const T& clamp( const T& v, const T& lo, const T& hi );
    		(1) (since C++17) 
    template< class T, class Compare >
constexpr const T& clamp( const T& v, const T& lo, const T& hi,
                          Compare comp );
    		(2) (since C++17)
    See More

    Returns a reference to the value in [lo, hi] that is closest to v.

    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
    comp - 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);

    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

    lo if v is less than lo, or hi if hi is less than v, otherwise v.

    Complexity

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

    Notes

    [edit]

    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 v rather than the bound.

    Feature-test macro Value Std Feature
    __cpp_lib_clamp 201603L (C++17) std::clamp

    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;
}

    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

    (C++20)
    		 clamps a value between a pair of boundary values
    (algorithm function object)[edit]
    		returns the smaller of the given values
    (function template & algorithm function object)[edit]
    (C++20)
    		returns the greater of the given values
    (function template & algorithm function object)[edit]
    (C++20)
    (C++20)
    		 checks if an integer value is in the range of a given integer type
    (function template) [edit]