header

<cfloat> (float.h)

Characteristics of floating-point types

This header describes the characteristics of floating types for the specific system and compiler implemetation used.

A floating-point number is composed of four elements:

a sign: either negative or non-negative
a base (or radix): which expresses the different numbers that can be represented with a single digit (2 for binary, 10 for decimal, 16 for hexadecimal, and so on...)
a significand (or mantissa): which is a series of digits of the aforementioned base. The number of digits in this series is what is known as precision.
an exponent (also known as characteristic, or scale): which represents the offset of the significand, affecting the value in the following way:
value of floating-point = significand x base^exponent, with its corresponding sign.

Macro constants

The following panel shows the name of the different values defined in this header and their minimal or maximal values for all implementations (particula rimplementations may have values greater or smaller, as specified):

When a group of macros exists prefixed by FLT_, DBL_ and LDBL_, the one beginning with FLT_ applies to the float type, the one with DBL_ to double and the one with LDBL_ to long double.

name	value	stands for	expresses
`FLT_RADIX`	`2` or greater	RADIX	Base for all floating-point types (`float`, `double` and `long double`).
`FLT_MANT_DIG` `DBL_MANT_DIG` `LDBL_MANT_DIG`		MANTissa DIGits	Precision of significand, i.e. the number of digits that conform the significand.
`FLT_DIG` `DBL_DIG` `LDBL_DIG`	`6` or greater `10` or greater `10` or greater	DIGits	Number of decimal digits that can be rounded into a floating-point and back without change in the number of decimal digits.
`FLT_MIN_EXP` `DBL_MIN_EXP` `LDBL_MIN_EXP`		MINimum EXPonent	Minimum negative integer value for the exponent that generates a normalized floating-point number.
`FLT_MIN_10_EXP` `DBL_MIN_10_EXP` `LDBL_MIN_10_EXP`	`-37` or smaller `-37` or smaller `-37` or smaller	MINimum base-10 EXPonent	Minimum negative integer value for the exponent of a base-10 expression that would generate a normalized floating-point number.
`FLT_MAX_EXP` `DBL_MAX_EXP` `LDBL_MAX_EXP`		MAXimum EXPonent	Maximum integer value for the exponent that generates a normalized floating-point number.
`FLT_MAX_10_EXP` `DBL_MAX_10_EXP` `LDBL_MAX_10_EXP`	`37` or greater `37` or greater `37` or greater	MAXimum base-10 EXPonent	Maximum integer value for the exponent of a base-10 expression that would generate a normalized floating-point number.
`FLT_MAX` `DBL_MAX` `LDBL_MAX`	`1E+37` or greater `1E+37` or greater `1E+37` or greater	MAXimum	Maximum finite representable floating-point number.
`FLT_EPSILON` `DBL_EPSILON` `LDBL_EPSILON`	`1E-5` or smaller `1E-9` or smaller `1E-9` or smaller	EPSILON	Difference between 1 and the least value greater than 1 that is representable.
`FLT_MIN` `DBL_MIN` `LDBL_MIN`	`1E-37` or smaller `1E-37` or smaller `1E-37` or smaller	MINimum	Minimum representable floating-point number.
`FLT_ROUNDS`		ROUND	Rounding behavior. Possible values: `-1` undetermined `0` toward zero `1` to nearest `2` toward positive infinity `3` toward negative infinity Applies to all floating-point types (`float`, `double` and `long double`).
`FLT_EVAL_METHOD`		EVALuation METHOD	Properties of the evaluation format. Possible values: `-1` undetermined `0` evaluate just to the range and precision of the type `1` evaluate `float` and `double` as `double`, and `long double` as `long double`. `2` evaluate all as `long double` Other negative values indicate an implementation-defined behavior. Applies to all floating-point types (`float`, `double` and `long double`).
`DECIMAL_DIG`		DECIMAL DIGits	Number of decimal digits that can be rounded into a floating-point type and back again to the same decimal digits, without loss in precision.

Compatibility

FLT_EVAL_METHOD and DECIMAL_DIG are defined for libraries complying with the C standard of 1999 or later (which only includes the C++ standard since 2011: C++11).

<cfloat> (float.h)

Macro constants

Compatibility

See also

C++

Reference

C library:

Containers:

Input/Output:

Multi-threading:

Other: