C Library  <float.h>
Introduction
The float.h header file of the C Standard Library contains a set of various platformdependent 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 floatingpoint number is composed of following four elements:
Component  Component Description 

S  sign ( +/ ) 
b  base or radix of the exponent representation, 2 for binary, 10 for decimal, 16 for hexadecimal, and so on... 
e  exponent, an integer between a minimum e_{min} and a maximum e_{max}. 
p  precision, the number of baseb digits in the significand 
Based on the above 4 components, a floating point will have its value as follows:
floatingpoint = ( S ) p x b^{e} or floatingpoint = (+/) precision x base^{exponent}
Library Macros
The following values are implementationspecific 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.
Macro  Description 

FLT_ROUNDS  Defines the rounding mode for floating point addition and it can have any of the following values:

FLT_RADIX 2  This defines the base radix representation of the exponent. A base2 is binary, base10 is the normal decimal representation, base16 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 (base10) 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 floatingpoint value. 
FLT_EPSILON 1E5 DBL_EPSILON 1E9 LDBL_EPSILON 1E9  These macros define the least significant digit representable. 
FLT_MIN 1E37 DBL_MIN 1E37 LDBL_MIN 1E37  These macros define the minimum floatingpoint 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 = 1.1754943508e38 The number of digits in the number = 7.2996655210e312