C Pocket Reference

Range and Precision of Real Floating Types

The macros listed in Table 1-26 are defined in the header file float.h to represent the range and the precision of the types float , double , and long double . The macro names are formed using the prefixes FLT for float, DBL for double, and LDBL for long double. The macros FLT_RADIX and FLT_ROUNDS apply to all three floating types.

Table 1-26. Macros for floating types in float.h

Macro name	Purpose
FLT_RADIX	Base (or radix) of the exponential notation
FLT_ROUNDS	Indicates how rounding is performed on values that cannot be represented exactly: -1 = undetermined 0 = towards zero, 1 = towards the nearest representable value 2 = upwards 3 = downwards
FLT_MANT_DIG DBL_MANT_DIG LDBL_MANT_DIG	The number of digits in the mantissa to base FLT_RADIX
FLT_MIN_EXP DBL_MIN_EXP LDBL_MIN_EXP	Minimum value of the exponent to base FLT_RADIX
FLT_MAX_EXP DBL_MAX_EXP LDBL_MAX_EXP	Maximum value of the exponent to base FLT_RADIX

The macros listed in Table 1-26 document the range and precision of all real floating types. In actual programs, such information is most often needed for decimal (base 10) notation. Accordingly, you can use the macros for type float listed Table 1-27, and which are defined in float.h.

Table 1-27. Limits for the type float

Macro name	Purpose
FLT_DIG	Precision as a number of decimal digits
FLT_MIN_10_EXP	Minimum negative exponent to base 10
FLT_MAX_10_EXP	Maximum positive exponent to base 10 ...