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std::clamp() algorithm

// (1)
template< class T >
constexpr const T& clamp( const T& v, const T& lo, const T& hi );

// (2)
template< class T, class Compare >
constexpr const T& clamp( const T& v, const T& lo, const T& hi, Compare comp );
  • If v compares less than lo, returns lo.

  • Otherwise, if v compares more than hi, returns hi.

  • Otherwise returns v.

  • (1) Uses operator< to compare the values.

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

Undefined Behaviour

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.

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.

bool cmp(const Type1 &a, const Type2 &b);
  • The signature does not need to have const&, but must not modify arguments.
  • Must accept all values of type (possibly const) Type and Type2, regardless of value category (so Type1& is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy (od 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

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.

Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

  • If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

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

Undefined Behaviour

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.

Examples

Main.cpp
#include <algorithm>
#include <cstdint>
#include <iomanip>
#include <iostream>

int main()
{
std::cout << " raw clamped to int8_t clamped to uint8_t\n";
for (const int 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
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.

std::clamp() algorithm

// (1)
template< class T >
constexpr const T& clamp( const T& v, const T& lo, const T& hi );

// (2)
template< class T, class Compare >
constexpr const T& clamp( const T& v, const T& lo, const T& hi, Compare comp );
  • If v compares less than lo, returns lo.

  • Otherwise, if v compares more than hi, returns hi.

  • Otherwise returns v.

  • (1) Uses operator< to compare the values.

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

Undefined Behaviour

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.

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.

bool cmp(const Type1 &a, const Type2 &b);
  • The signature does not need to have const&, but must not modify arguments.
  • Must accept all values of type (possibly const) Type and Type2, regardless of value category (so Type1& is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy (od 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

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.

Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

  • If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

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

Undefined Behaviour

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.

Examples

Main.cpp
#include <algorithm>
#include <cstdint>
#include <iomanip>
#include <iostream>

int main()
{
std::cout << " raw clamped to int8_t clamped to uint8_t\n";
for (const int 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
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.