Standard library header <cfloat>

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

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

Macros

Characteristics
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_SUBNORMDBL_HAS_SUBNORMLDBL_HAS_SUBNORM (C++17)(deprecated in C++26)

specifies whether the type supports subnormal (denormal) numbers: -1 – indeterminable, 0 – absent, 1 – present (macro constant)

FLT_RADIX	the radix (integer base) used by the representation of all three floating-point types (macro constant)
FLT_MANT_DIGDBL_MANT_DIGLDBL_MANT_DIG	number of base FLT_RADIX digits that can be represented without losing precision for float, double and longdouble respectively (macro constant)
FLT_DECIMAL_DIGDBL_DECIMAL_DIGLDBL_DECIMAL_DIG (C++17)	conversion from float/double/longdouble 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 (macro constant)

DECIMAL_DIG (C++11)(deprecated in C++26)

conversion from longdouble to decimal with at least DECIMAL_DIG digits and back to longdouble is the identity conversion: this is the decimal precision required to serialize/deserialize a longdouble (macro constant)

FLT_DIGDBL_DIGLDBL_DIG	number of decimal digits that are guaranteed to be preserved in text → float/double/longdouble → text roundtrip without change due to rounding or overflow (macro constant)
FLT_MIN_EXPDBL_MIN_EXPLDBL_MIN_EXP	minimum negative integer such that FLT_RADIX raised by power one less than that integer is a normalized float, double and longdouble respectively (macro constant)
FLT_MIN_10_EXPDBL_MIN_10_EXPLDBL_MIN_10_EXP	minimum negative integer such that 10 raised to that power is a normalized float, double and longdouble respectively (macro constant)
FLT_MAX_EXPDBL_MAX_EXPLDBL_MAX_EXP	maximum positive integer such that FLT_RADIX raised by power one less than that integer is a representable finite float, double and longdouble respectively (macro constant)
FLT_MAX_10_EXPDBL_MAX_10_EXPLDBL_MAX_10_EXP	maximum positive integer such that 10 raised to that power is a representable finite float, double and longdouble respectively (macro constant)
FLT_MAXDBL_MAXLDBL_MAX	maximum finite value of float, double and longdouble respectively (macro constant)
FLT_EPSILONDBL_EPSILONLDBL_EPSILON	difference between 1.0 and the next representable value for float, double and longdouble respectively (macro constant)
FLT_MINDBL_MINLDBL_MIN	minimum normalized positive value of float, double and longdouble respectively (macro constant)
FLT_TRUE_MINDBL_TRUE_MINLDBL_TRUE_MIN (C++17)	minimum positive value of float, double and longdouble respectively (macro constant)
Special values (since C++26)
INFINITY (C++11)	evaluates to positive infinity (if exists) (macro constant)
NAN (C++11)	evaluates to a quiet NaN of type float (if exists) (macro constant)
FLT_SNANDBL_SNANLDBL_SNAN (C++26)	evaluates to a signaling NaN of float, double and longdouble respectively (if exists) (macro constant)

Synopsis

// all freestanding
#define __STDC_VERSION_FLOAT_H__ 202311L

#define FLT_ROUNDS       /* see description */
#define FLT_EVAL_METHOD  /* see description */
#define FLT_RADIX        /* see description */
#define INFINITY         /* see description */
#define NAN              /* see description */
#define FLT_SNAN         /* see description */
#define DBL_SNAN         /* see description */
#define LDBL_SNAN        /* see description */
#define FLT_MANT_DIG     /* see description */
#define DBL_MANT_DIG     /* see description */
#define LDBL_MANT_DIG    /* see description */
#define FLT_DECIMAL_DIG  /* see description */
#define DBL_DECIMAL_DIG  /* see description */
#define LDBL_DECIMAL_DIG /* see description */
#define FLT_DIG          /* see description */
#define DBL_DIG          /* see description */
#define LDBL_DIG         /* see description */
#define FLT_MIN_EXP      /* see description */
#define DBL_MIN_EXP      /* see description */
#define LDBL_MIN_EXP     /* see description */
#define FLT_MIN_10_EXP   /* see description */
#define DBL_MIN_10_EXP   /* see description */
#define LDBL_MIN_10_EXP  /* see description */
#define FLT_MAX_EXP      /* see description */
#define DBL_MAX_EXP      /* see description */
#define LDBL_MAX_EXP     /* see description */
#define FLT_MAX_10_EXP   /* see description */
#define DBL_MAX_10_EXP   /* see description */
#define LDBL_MAX_10_EXP  /* see description */
#define FLT_MAX          /* see description */
#define DBL_MAX          /* see description */
#define LDBL_MAX         /* see description */
#define FLT_EPSILON      /* see description */
#define DBL_EPSILON      /* see description */
#define LDBL_EPSILON     /* see description */
#define FLT_MIN          /* see description */
#define DBL_MIN          /* see description */
#define LDBL_MIN         /* see description */
#define FLT_TRUE_MIN     /* see description */
#define DBL_TRUE_MIN     /* see description */
#define LDBL_TRUE_MIN    /* see description */

See also

C documentation for Limits of floating-point types