# C numeric limits interface

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See also std::numeric_limits interface.

### Limits of integer types

##### Limits of core language integer types
Defined in header `<climits>`
CHAR_BIT | number of bits in a byte (macro constant)
MB_LEN_MAX | maximum number of bytes in a multibyte character (macro constant)
CHAR_MIN | minimum value of char (macro constant)
CHAR_MAX | maximum value of char (macro constant)
SCHAR_MIN SHRT_MIN INT_MIN LONG_MIN LLONG_MIN (C++11) | minimum value of signed char, short, int, long and long long respectively (macro constant)
SCHAR_MAX SHRT_MAX INT_MAX LONG_MAX LLONG_MAX (C++11) | maximum value of signed char, short, int, long and long long respectively (macro constant)
UCHAR_MAX USHRT_MAX UINT_MAX ULONG_MAX ULLONG_MAX (C++11) | maximum value of unsigned char, unsigned short, unsigned int, unsigned long and unsigned long long respectively (macro constant)
Defined in header `<cwchar>`
Defined in header `<cstdint>`
WCHAR_MIN (C++11) | minimum value of wchar_t (macro constant)
WCHAR_MAX (C++11) | maximum value of wchar_t (macro constant)
##### Limits of library type aliases
Defined in header `<cstdint>`
PTRDIFF_MIN (C++11) | minimum value of std::ptrdiff_t (macro constant)
PTRDIFF_MAX (C++11) | maximum value of std::ptrdiff_t (macro constant)
SIZE_MAX (C++11) | maximum value of std::size_t (macro constant)
SIG_ATOMIC_MIN (C++11) | minimum value of std::sig_atomic_t (macro constant)
SIG_ATOMIC_MAX (C++11) | maximum value of std::sig_atomic_t (macro constant)
WINT_MIN (C++11) | minimum value of `std::wint_t` (macro constant)
WINT_MAX (C++11) | maximum value of `std::wint_t` (macro constant)

#### Notes

The types of these constants, other than CHAR_BIT and MB_LEN_MAX, are required to match the results of the integral promotions as applied to objects of the types they describe: CHAR_MAX may have type int or unsigned int, but never char. Similarly USHRT_MAX may not be of an unsigned type: its type may be int.

A freestanding implementation may lack std::sig_atomic_t and/or `std::wint_t` typedef names, in which case the `SIG_ATOMIC_*` and/or `WINT_*` macros are correspondingly absent.

#### Example

Run this code

    #include <climits>
    #include <cstdint>
    #include <iomanip>
    #include <iostream>

    int main()
    {
        constexpr int w = 14;
        std::cout << std::left;
    #   define COUT(x) std::cout << std::setw(w) << #x << " = " << x << '\n'

        COUT( CHAR_BIT       );
        COUT( MB_LEN_MAX     );
        COUT( CHAR_MIN       );
        COUT( CHAR_MAX       );
        COUT( SCHAR_MIN      );
        COUT( SHRT_MIN       );
        COUT( INT_MIN        );
        COUT( LONG_MIN       );
        COUT( LLONG_MIN      );
        COUT( SCHAR_MAX      );
        COUT( SHRT_MAX       );
        COUT( INT_MAX        );
        COUT( LONG_MAX       );
        COUT( LLONG_MAX      );
        COUT( UCHAR_MAX      );
        COUT( USHRT_MAX      );
        COUT( UINT_MAX       );
        COUT( ULONG_MAX      );
        COUT( ULLONG_MAX     );
        COUT( PTRDIFF_MIN    );
        COUT( PTRDIFF_MAX    );
        COUT( SIZE_MAX       );
        COUT( SIG_ATOMIC_MIN );
        COUT( SIG_ATOMIC_MAX );
        COUT( WCHAR_MIN      );
        COUT( WCHAR_MAX      );
        COUT( WINT_MIN       );
        COUT( WINT_MAX       );
    }

Possible output:

    CHAR_BIT       = 8
    MB_LEN_MAX     = 16
    CHAR_MIN       = -128
    CHAR_MAX       = 127
    SCHAR_MIN      = -128
    SHRT_MIN       = -32768
    INT_MIN        = -2147483648
    LONG_MIN       = -9223372036854775808
    LLONG_MIN      = -9223372036854775808
    SCHAR_MAX      = 127
    SHRT_MAX       = 32767
    INT_MAX        = 2147483647
    LONG_MAX       = 9223372036854775807
    LLONG_MAX      = 9223372036854775807
    UCHAR_MAX      = 255
    USHRT_MAX      = 65535
    UINT_MAX       = 4294967295
    ULONG_MAX      = 18446744073709551615
    ULLONG_MAX     = 18446744073709551615
    PTRDIFF_MIN    = -9223372036854775808
    PTRDIFF_MAX    = 9223372036854775807
    SIZE_MAX       = 18446744073709551615
    SIG_ATOMIC_MIN = -2147483648
    SIG_ATOMIC_MAX = 2147483647
    WCHAR_MIN      = -2147483648
    WCHAR_MAX      = 2147483647
    WINT_MIN       = 0
    WINT_MAX       = 4294967295

### Limits of floating-point types

Defined in header `<cfloat>`
FLT_RADIX | the radix (integer base) used by the representation of all three floating-point types (macro constant)
DECIMAL_DIG (C++11) | conversion from long double to decimal with at least DECIMAL_DIG digits and back to long double is the identity conversion: this is the decimal precision required to serialize/deserialize a long double (see also std::numeric_limits::max_digits10) (macro constant)
FLT_DECIMAL_DIG DBL_DECIMAL_DIG LDBL_DECIMAL_DIG (C++17) | conversion from float/double/long double to decimal with at least FLT_DECIMAL_DIG/DBL_DECIMAL_DIG/LDBL_DECIMAL_DIG digits and back is the identity conversion: this is the decimal precision required to serialize/deserialize a floating-point value (see also std::numeric_limits::max_digits10). Defined to at least 6, 10, and 10 respectively, or 9 for IEEE float and 17 for IEEE double. (macro constant)
FLT_MIN DBL_MIN LDBL_MIN | minimum normalized positive value of float, double and long double respectively (macro constant)
FLT_TRUE_MIN DBL_TRUE_MIN LDBL_TRUE_MIN (C++17) | minimum positive value of float, double and long double respectively (macro constant)
FLT_MAX DBL_MAX LDBL_MAX | maximum finite value of float, double and long double respectively (macro constant)
FLT_EPSILON DBL_EPSILON LDBL_EPSILON | difference between 1.0 and the next representable value for float, double and long double respectively (macro constant)
FLT_DIG DBL_DIG LDBL_DIG | number of decimal digits that are guaranteed to be preserved in text → float/double/long double → text roundtrip without change due to rounding or overflow (see std::numeric_limits::digits10 for explanation) (macro constant)
FLT_MANT_DIG DBL_MANT_DIG LDBL_MANT_DIG | number of base FLT_RADIX digits that can be represented without losing precision for float, double and long double respectively (macro constant)
FLT_MIN_EXP DBL_MIN_EXP LDBL_MIN_EXP | minimum negative integer such that FLT_RADIX raised by power one less than that integer is a normalized float, double and long double respectively (macro constant)
FLT_MIN_10_EXP DBL_MIN_10_EXP LDBL_MIN_10_EXP | minimum negative integer such that 10 raised to that power is a normalized float, double and long double respectively (macro constant)
FLT_MAX_EXP DBL_MAX_EXP LDBL_MAX_EXP | maximum positive integer such that FLT_RADIX raised by power one less than that integer is a representable finite float, double and long double respectively (macro constant)
FLT_MAX_10_EXP DBL_MAX_10_EXP LDBL_MAX_10_EXP | maximum positive integer such that 10 raised to that power is a representable finite float, double and long double respectively (macro constant)
FLT_ROUNDS | default rounding mode of floating-point arithmetic (macro constant)
FLT_EVAL_METHOD (C++11) | specifies in what precision all arithmetic operations are done (macro constant)
FLT_HAS_SUBNORM DBL_HAS_SUBNORM LDBL_HAS_SUBNORM (C++17) | specifies whether the type supports subnormal (denormal) numbers: -1 – indeterminable, ​0​ – absent, 1 – present (macro constant)

#### Example

Run this code

    #include <cfloat>
    #include <iomanip>
    #include <iostream>

    int main()
    {
        int w = 16;
        std::cout << std::left; // std::cout << std::setprecision(53);
    #   define COUT(x) std::cout << std::setw(w) << #x << " = " << x << '\n'

        COUT( FLT_RADIX        );
        COUT( DECIMAL_DIG      );
        COUT( FLT_DECIMAL_DIG  );
        COUT( DBL_DECIMAL_DIG  );
        COUT( LDBL_DECIMAL_DIG );
        COUT( FLT_MIN          );
        COUT( DBL_MIN          );
        COUT( LDBL_MIN         );
        COUT( FLT_TRUE_MIN     );
        COUT( DBL_TRUE_MIN     );
        COUT( LDBL_TRUE_MIN    );
        COUT( FLT_MAX          );
        COUT( DBL_MAX          );
        COUT( LDBL_MAX         );
        COUT( FLT_EPSILON      );
        COUT( DBL_EPSILON      );
        COUT( LDBL_EPSILON     );
        COUT( FLT_DIG          );
        COUT( DBL_DIG          );
        COUT( LDBL_DIG         );
        COUT( FLT_MANT_DIG     );
        COUT( DBL_MANT_DIG     );
        COUT( LDBL_MANT_DIG    );
        COUT( FLT_MIN_EXP      );
        COUT( DBL_MIN_EXP      );
        COUT( LDBL_MIN_EXP     );
        COUT( FLT_MIN_10_EXP   );
        COUT( DBL_MIN_10_EXP   );
        COUT( LDBL_MIN_10_EXP  );
        COUT( FLT_MAX_EXP      );
        COUT( DBL_MAX_EXP      );
        COUT( LDBL_MAX_EXP     );
        COUT( FLT_MAX_10_EXP   );
        COUT( DBL_MAX_10_EXP   );
        COUT( LDBL_MAX_10_EXP  );
        COUT( FLT_ROUNDS       );
        COUT( FLT_EVAL_METHOD  );
        COUT( FLT_HAS_SUBNORM  );
        COUT( DBL_HAS_SUBNORM  );
        COUT( LDBL_HAS_SUBNORM );
    }

Possible output:

    FLT_RADIX        = 2
    DECIMAL_DIG      = 21
    FLT_DECIMAL_DIG  = 9
    DBL_DECIMAL_DIG  = 17
    LDBL_DECIMAL_DIG = 21
    FLT_MIN          = 1.17549e-38
    DBL_MIN          = 2.22507e-308
    LDBL_MIN         = 3.3621e-4932
    FLT_TRUE_MIN     = 1.4013e-45
    DBL_TRUE_MIN     = 4.94066e-324
    LDBL_TRUE_MIN    = 3.6452e-4951
    FLT_MAX          = 3.40282e+38
    DBL_MAX          = 1.79769e+308
    LDBL_MAX         = 1.18973e+4932
    FLT_EPSILON      = 1.19209e-07
    DBL_EPSILON      = 2.22045e-16
    LDBL_EPSILON     = 1.0842e-19
    FLT_DIG          = 6
    DBL_DIG          = 15
    LDBL_DIG         = 18
    FLT_MANT_DIG     = 24
    DBL_MANT_DIG     = 53
    LDBL_MANT_DIG    = 64
    FLT_MIN_EXP      = -125
    DBL_MIN_EXP      = -1021
    LDBL_MIN_EXP     = -16381
    FLT_MIN_10_EXP   = -37
    DBL_MIN_10_EXP   = -307
    LDBL_MIN_10_EXP  = -4931
    FLT_MAX_EXP      = 128
    DBL_MAX_EXP      = 1024
    LDBL_MAX_EXP     = 16384
    FLT_MAX_10_EXP   = 38
    DBL_MAX_10_EXP   = 308
    LDBL_MAX_10_EXP  = 4932
    FLT_ROUNDS       = 1
    FLT_EVAL_METHOD  = 0
    FLT_HAS_SUBNORM  = 1
    DBL_HAS_SUBNORM  = 1
    LDBL_HAS_SUBNORM = 1

### 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 416 | C++98 | it was unclear whether the types of the macros in `<climits>` are guaranteed to match the type to which they refer (C++ refers to C, and C says no) | clarified as not guaranteed

### See also

- Fixed width integer types
- Arithmetic types
- C++ type system overview
- Type support (basic types, RTTI, type traits)

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