# Standard library header <cfloat>

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This header was originally in the C standard library as `<float.h>`.

This header is part of the type support library, in particular it's part of the C numeric limits interface.

### Macros

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)

### Synopsis

    #define FLT_ROUNDS           /* see definition */
    #define FLT_EVAL_METHOD      /* see definition */
    #define FLT_HAS_SUBNORM      /* see definition */
    #define DBL_HAS_SUBNORM      /* see definition */
    #define LDBL_HAS_SUBNORM     /* see definition */
    #define FLT_RADIX            /* see definition */
    #define FLT_MANT_DIG         /* see definition */
    #define DBL_MANT_DIG         /* see definition */
    #define LDBL_MANT_DIG        /* see definition */
    #define FLT_DECIMAL_DIG      /* see definition */
    #define DBL_DECIMAL_DIG      /* see definition */
    #define LDBL_DECIMAL_DIG     /* see definition */
    #define DECIMAL_DIG          /* see definition */
    #define FLT_DIG              /* see definition */
    #define DBL_DIG              /* see definition */
    #define LDBL_DIG             /* see definition */
    #define FLT_MIN_EXP          /* see definition */
    #define DBL_MIN_EXP          /* see definition */
    #define LDBL_MIN_EXP         /* see definition */
    #define FLT_MIN_10_EXP       /* see definition */
    #define DBL_MIN_10_EXP       /* see definition */
    #define LDBL_MIN_10_EXP      /* see definition */
    #define FLT_MAX_EXP          /* see definition */
    #define DBL_MAX_EXP          /* see definition */
    #define LDBL_MAX_EXP         /* see definition */
    #define FLT_MAX_10_EXP       /* see definition */
    #define DBL_MAX_10_EXP       /* see definition */
    #define LDBL_MAX_10_EXP      /* see definition */
    #define FLT_MAX              /* see definition */
    #define DBL_MAX              /* see definition */
    #define LDBL_MAX             /* see definition */
    #define FLT_EPSILON          /* see definition */
    #define DBL_EPSILON          /* see definition */
    #define LDBL_EPSILON         /* see definition */
    #define FLT_MIN              /* see definition */
    #define DBL_MIN              /* see definition */
    #define LDBL_MIN             /* see definition */
    #define FLT_TRUE_MIN         /* see definition */
    #define DBL_TRUE_MIN         /* see definition */
    #define LDBL_TRUE_MIN        /* see definition */

### See also

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