Standard library header <float.h>

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

Macros

Characteristics
FLT_ROUNDS	default rounding mode of floating-point arithmetic (macro constant)
FLT_EVAL_METHOD (C99)	specifies in what precision all arithmetic operations are done (macro constant)

FLT_HAS_SUBNORMDBL_HAS_SUBNORMLDBL_HAS_SUBNORM (C11)(deprecated in C23)

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 (C11)	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 (C99)(deprecated in C23)

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 (C11)	minimum positive value of float, double and longdouble respectively (macro constant)
Special values (since C23)
INFINITY (C99)	evaluates to positive infinity (if exists) (macro constant)
NAN (C99)	evaluates to a quiet NaN of type float (if exists) (macro constant)
FLT_SNANDBL_SNANLDBL_SNAN (C23)	evaluates to a signaling NaN of float, double and longdouble respectively (if exists) (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 */
#define INFINITY             /* see definition */
#define NAN                  /* see definition */
#define FLT_SNAN             /* see definition */
#define DBL_SNAN             /* see definition */
#define LDBL_SNAN            /* see definition */