C Library - <float.h>

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Introduction

The float.h header file of the C Standard Library contains a set of various platform-dependent constants related to floating point values. These constants are proposed by ANSI C. They allow making more portable programs. Before checking all the constants, it is good to understand that floating-point number is composed of following four elements:

Component Component Description
Ssign ( +/- )
bbase or radix of the exponent representation, 2 for binary, 10 for decimal, 16 for hexadecimal, and so on...
eexponent, an integer between a minimum emin and a maximum emax.
pprecision, the number of base-b digits in the significand

Based on the above 4 components, a floating point will have its value as follows:

floating-point = ( S ) p x be

or

floating-point = (+/-) precision x baseexponent

Library Macros

The following values are implementation-specific and defined with the #define directive, but these values may not be any lower than what is given here. Note that in all instances FLT refers to type float, DBL refers to double, and LDBL refers to long double.

MacroDescription
FLT_ROUNDSDefines the rounding mode for floating point addition and it can have any of the following values:
  • -1 - indeterminable

  • 0 - toward zero

  • 1 - to nearest

  • 2 - toward positive infinity

  • 3 - toward negative infinity

FLT_RADIX 2This defines the base radix representation of the exponent. A base-2 is binary, base-10 is the normal decimal representation, base-16 is Hex.

FLT_MANT_DIG

DBL_MANT_DIG

LDBL_MANT_DIG

These macros define the number of digits in the number (in the FLT_RADIX base).

FLT_DIG 6

DBL_DIG 10

LDBL_DIG 10

These macros define the maximum number decimal digits (base-10) that can be represented without change after rounding.

FLT_MIN_EXP

DBL_MIN_EXP

LDBL_MIN_EXP

These macros define the minimum negative integer value for an exponent in base FLT_RADIX.

FLT_MIN_10_EXP -37

DBL_MIN_10_EXP -37

LDBL_MIN_10_EXP -37

These macros define the minimum negative integer value for an exponent in base 10.

FLT_MAX_EXP

DBL_MAX_EXP

LDBL_MAX_EXP

These macros define the maximum integer value for an exponent in base FLT_RADIX.

FLT_MAX_10_EXP +37

DBL_MAX_10_EXP +37

LDBL_MAX_10_EXP +37

These macros define the maximum integer value for an exponent in base 10.

FLT_MAX 1E+37

DBL_MAX 1E+37

LDBL_MAX 1E+37

These macros define the maximum finite floating-point value.

FLT_EPSILON 1E-5

DBL_EPSILON 1E-9

LDBL_EPSILON 1E-9

These macros define the least significant digit representable.

FLT_MIN 1E-37

DBL_MIN 1E-37

LDBL_MIN 1E-37

These macros define the minimum floating-point value..

Example

The following example shows the usage of few of the constants defined in float.h file.

#include <stdio.h>
#include <float.h>

int main()
{
   printf("The maximum value of float = %.10e\n", FLT_MAX);
   printf("The minimum value of float = %.10e\n", FLT_MIN);

   printf("The number of digits in the number = %.10e\n", FLT_MANT_DIG);
}

Let us compile and run the above program, this will produce the following result:

The maximum value of float = 3.4028234664e+38
The minimum value of float = 1.1754943508e-38
The number of digits in the number = 7.2996655210e-312


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