NAME¶

std::numeric_limits - std::numeric_limits

Synopsis¶

Defined in header <limits>
template< class T > class numeric_limits;

The std::numeric_limits class template provides a standardized way to query various
properties of arithmetic types (e.g. the largest possible value for type int is
std::numeric_limits<int>::max()).

This information is provided via specializations of the std::numeric_limits
template. The standard library makes available specializations for all arithmetic
types (only lists the specializations for cv-unqualified arithmetic types):

Defined in header <limits>
template<> class numeric_limits<bool>;
template<> class numeric_limits<char>;
template<> class numeric_limits<signed char>;
template<> class numeric_limits<unsigned char>;
template<> class numeric_limits<wchar_t>;
template<> class numeric_limits<char8_t>; (since C++20)
template<> class numeric_limits<char16_t>; (since C++11)
template<> class numeric_limits<char32_t>; (since C++11)
template<> class numeric_limits<short>;
template<> class numeric_limits<unsigned short>;
template<> class numeric_limits<int>;
template<> class numeric_limits<unsigned int>;
template<> class numeric_limits<long>;
template<> class numeric_limits<unsigned long>;
template<> class numeric_limits<long long>; (since C++11)
template<> class numeric_limits<unsigned long long>; (since C++11)
template<> class numeric_limits<float>;
template<> class numeric_limits<double>;
template<> class numeric_limits<long double>;

The value of each member of a specialization of std::numeric_limits on a
cv-qualified type cv T is equal to the value of the corresponding member of the
specialization on the unqualified type T. For example,
std::numeric_limits<int>::digits is equal to std::numeric_limits<const int>::digits.

Aliases of arithmetic types (such as std::size_t or std::streamsize) may also be
examined with the std::numeric_limits type traits.

Non-arithmetic standard types, such as std::complex<T> or std::nullptr_t, do not
have specializations.

If the implementation defines any integer-class types, specializations (since C++20)
of std::numeric_limits must also be provided for them.

Implementations may provide specializations of std::numeric_limits for
implementation-specific types: e.g. GCC provides std::numeric_limits<__int128>.
Non-standard libraries may add specializations for library-provided types, e.g.
OpenEXR provides std::numeric_limits<half> for a 16-bit floating-point type.

Template parameters¶

T - a type to retrieve numeric properties for

Member constants¶

is_specialized identifies types for which std::numeric_limits is specialized
[static] (public static member constant)
is_signed identifies signed types
[static] (public static member constant)
is_integer identifies integer types
[static] (public static member constant)
is_exact identifies exact types
[static] (public static member constant)
has_infinity identifies floating-point types that can represent the special
[static] value "positive infinity"
(public static member constant)
has_quiet_NaN identifies floating-point types that can represent the special
[static] value "quiet not-a-number" (NaN)
(public static member constant)
has_signaling_NaN identifies floating-point types that can represent the special
[static] value "signaling not-a-number" (NaN)
(public static member constant)
has_denorm identifies the denormalization style used by the floating-point
[static] type
(public static member constant)
has_denorm_loss identifies the floating-point types that detect loss of precision
[static] as denormalization loss rather than inexact result
(public static member constant)
round_style identifies the rounding style used by the type
[static] (public static member constant)
is_iec559 identifies the IEC 559/IEEE 754 floating-point types
[static] (public static member constant)
is_bounded identifies types that represent a finite set of values
[static] (public static member constant)
is_modulo identifies types that handle overflows with modulo arithmetic
[static] (public static member constant)
digits number of radix digits that can be represented without change
[static] (public static member constant)
digits10 number of decimal digits that can be represented without change
[static] (public static member constant)
max_digits10 number of decimal digits necessary to differentiate all values of
[static] (C++11) this type
(public static member constant)
radix the radix or integer base used by the representation of the given
[static] type
(public static member constant)
min_exponent one more than the smallest negative power of the radix that is a
[static] valid normalized floating-point value
(public static member constant)
min_exponent10 the smallest negative power of ten that is a valid normalized
[static] floating-point value
(public static member constant)
max_exponent one more than the largest integer power of the radix that is a
[static] valid finite floating-point value
(public static member constant)
max_exponent10 the largest integer power of 10 that is a valid finite
[static] floating-point value
(public static member constant)
traps identifies types which can cause arithmetic operations to trap
[static] (public static member constant)
tinyness_before identifies floating-point types that detect tinyness before
[static] rounding
(public static member constant)

Member functions¶

min returns the smallest finite value of the given type
[static] (public static member function)
lowest returns the lowest finite value of the given type
[static] (C++11) (public static member function)
max returns the largest finite value of the given type
[static] (public static member function)
epsilon returns the difference between 1.0 and the next representable value
[static] of the given floating-point type
(public static member function)
round_error returns the maximum rounding error of the given floating-point type
[static] (public static member function)
infinity returns the positive infinity value of the given floating-point
[static] type
(public static member function)
quiet_NaN returns a quiet NaN value of the given floating-point type
[static] (public static member function)
signaling_NaN returns a signaling NaN value of the given floating-point type
[static] (public static member function)
denorm_min returns the smallest positive subnormal value of the given
[static] floating-point type
(public static member function)

Helper classes¶

float_round_style indicates floating-point rounding modes
(enum)
float_denorm_style indicates floating-point denormalization modes
(enum)

Relationship with C library macro constants¶

Specialization Members
std::numeric_limits<T> min() lowest() max() radix
where T is (C++11)
bool false false true 2
char CHAR_MIN CHAR_MIN CHAR_MAX 2
signed char SCHAR_MIN SCHAR_MIN SCHAR_MAX 2
unsigned char 0 0 UCHAR_MAX 2
wchar_t WCHAR_MIN WCHAR_MIN WCHAR_MAX 2
char8_t 0 0 UCHAR_MAX 2
char16_t 0 0 UINT_LEAST16_MAX 2
char32_t 0 0 UINT_LEAST32_MAX 2
short SHRT_MIN SHRT_MIN SHRT_MAX 2
signed short
unsigned short 0 0 USHRT_MAX 2
int INT_MIN INT_MIN INT_MAX 2
signed int
unsigned int 0 0 UINT_MAX 2
long LONG_MIN LONG_MIN LONG_MAX 2
signed long
unsigned long 0 0 ULONG_MAX 2
long long LLONG_MIN LLONG_MIN LLONG_MAX 2
signed long long
unsigned long long 0 0 ULLONG_MAX 2

Specialization Members std::numeric_limits<T> denorm_min() min() lowest() max() epsilon() digits digits10
where T is (C++11) float FLT_TRUE_MIN FLT_MIN -FLT_MAX FLT_MAX FLT_EPSILON FLT_MANT_DIG FLT_DIG double DBL_TRUE_MIN DBL_MIN -DBL_MAX DBL_MAX DBL_EPSILON DBL_MANT_DIG DBL_DIG long double LDBL_TRUE_MIN LDBL_MIN -LDBL_MAX LDBL_MAX LDBL_EPSILON LDBL_MANT_DIG LDBL_DIG

Specialization Members (continue) std::numeric_limits<T>
where T is min_exponent min_exponent10 max_exponent max_exponent10 radix float FLT_MIN_EXP FLT_MIN_10_EXP FLT_MAX_EXP FLT_MAX_10_EXP FLT_RADIX double DBL_MIN_EXP DBL_MIN_10_EXP DBL_MAX_EXP DBL_MAX_10_EXP FLT_RADIX long double LDBL_MIN_EXP LDBL_MIN_10_EXP LDBL_MAX_EXP LDBL_MAX_10_EXP FLT_RADIX

Example¶

// Run this code

#include <iostream>
#include <limits>

int main()
{
std::cout << "type\t│ lowest()\t│ min()\t\t│ max()\n"
<< "bool\t│ "
<< std::numeric_limits<bool>::lowest() << "\t\t│ "
<< std::numeric_limits<bool>::min() << "\t\t│ "
<< std::numeric_limits<bool>::max() << '\n'
<< "uchar\t│ "
<< +std::numeric_limits<unsigned char>::lowest() << "\t\t│ "
<< +std::numeric_limits<unsigned char>::min() << "\t\t│ "
<< +std::numeric_limits<unsigned char>::max() << '\n'
<< "int\t│ "
<< std::numeric_limits<int>::lowest() << "\t│ "
<< std::numeric_limits<int>::min() << "\t│ "
<< std::numeric_limits<int>::max() << '\n'
<< "float\t│ "
<< std::numeric_limits<float>::lowest() << "\t│ "
<< std::numeric_limits<float>::min() << "\t│ "
<< std::numeric_limits<float>::max() << '\n'
<< "double\t│ "
<< std::numeric_limits<double>::lowest() << "\t│ "
<< std::numeric_limits<double>::min() << "\t│ "
<< std::numeric_limits<double>::max() << '\n';
}

Possible output:¶

type │ lowest() │ min() │ max()
bool │ 0 │ 0 │ 1
uchar │ 0 │ 0 │ 255
int │ -2147483648 │ -2147483648 │ 2147483647
float │ -3.40282e+38 │ 1.17549e-38 │ 3.40282e+38
double │ -1.79769e+308 │ 2.22507e-308 │ 1.79769e+308

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 201 C++98 specializations for all fundamental types excluded non-arithmetic
need to be provided types
it was unclear whether the
std::numeric_limits
LWG 559 C++98 specialization for a cv-qualified type they have the
behaves as the same as same behavior
the corresponding specialization for the
cv-unqualified type

See also¶

* Fixed width integer types
* Arithmetic types
* C++ type system overview
* Type support (basic types, RTTI, type traits)
* C numeric limits interface