std::clamp

 

C++

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Technical Specifications

 

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C library
qsort	bsearch

 

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)

1) If v compares less than hi, returns the larger of v and lo, otherwise returns the smaller of v and hi. Uses operator< to compare the values.

2) Same as (1), but uses comp to compare the values.

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 lo is less than v and v is less than hi. The signature of the comparison function should be equivalent to the following:  bool cmp(const Type1 &a, const Type2 &b); The signature does not need to have const &, but the function object must not modify the objects passed to it. 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).

Return value

Reference to v if it is between the bounds, lo if v is smaller than lo, and hi if v is larger than hi.

If v compares equivalent to either bound, returns v.

Complexity

1) 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, std::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, hi) ? std::max(v, lo, comp) : std::min(v, hi, comp); }

Notes

Capturing the result of std::clamp by reference if one of the parameters is rvalue produces a dangling reference if that parameter is returned:

int n = -1;
const int& r = std::clamp(n, 0, 255);
// r is dangling

Example

Run this code

#include <cstdint>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <random>
 
int main()
{
    std::mt19937 g(std::random_device{}());
    std::uniform_int_distribution<> d(-300, 300);
    std::cout << " raw   clamped to int8_t   clamped to uint8_t\n";
    for(int n = 0; n < 5; ++n) {
        int v = d(g);
        std::cout << std::setw(4) << v
                  << std::setw(20) << std::clamp(v, INT8_MIN, INT8_MAX)
                  << std::setw(21) << std::clamp(v, 0, UINT8_MAX) << '\n';
    }
}

Possible output:

.raw   clamped to int8_t   clamped to uint8_t
 168                 127                  168
 128                 127                  128
-137                -128                    0
  40                  40                   40
 -66                 -66                    0

See also

min	returns the smaller of the given values (function template)
max	returns the greater of the given values (function template)