The <float.h> header file in C defines platform-dependent and implementation-specific characteristics of floating-point types. These macros provide information about the precision, range, rounding behavior, and representation of float, double, and long double.
Floating-Point Representation
A floating-point number consists of four main parts:
- Sign: Indicates whether the number is positive or negative.
- Base (Radix): Represents the base used for the exponent representation, such as 2 for binary, 10 for decimal, and 16 for hexadecimal.
- Mantissa (Significand): Represents a sequence of digits in the given base. The number of significant digits determines the precision.
- Exponent: Determines the scale of the floating-point number and has a minimum and maximum range.
Value of floating point = Âą precision X baseexponent
Floating-Point Macro Constants
Macro constants Library macros are hardware-specific values for the floating-point types.FLT implies type float, DBL implies double, and LDBL implies long double, DIG implies digits, MANT implies mantissa, EXP implies exponent.
1. FLT_RADIX: Base for all floating-point types
Minimum value is 2
2. FLT_DIG: 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.
Minimum value is 6
3. DBL_DIG or LDBL_DIG: Number of decimal digits that can be rounded into a floating-point and back without change in the number of decimal digits.
Minimum value is 10
4. DECIMAL_DIG: Decimal digits needed to represent floating-point value
No Minimum value
5. FLT_MANT_DIG or DBL_MANT_DIG or LDBL_MANT_DIG: Precision of mantissa i.e. the number of digits that conform the significand.
No Minimum value
6. FLT_MIN_EXP or DBL_MIN_EXP or LDBL_MIN_EXP: Minimum negative integer value for the exponent that generates a normalized floating-point number.
No Minimum value
7. FLT_MIN_10_EXP or DBL_MIN_10_EXP or LDBL_MIN_10_EXP: Minimum negative integer value for the exponent of a base-10 expression that would generate a normalized floating-point number.
Maximum value is -37
8. FLT_MAX_EXP or DBL_MAX_EXP or LDBL_MAX_EXP: Maximum integer value for the exponent that generates a normalized floating-point number. \
No Minimum value
9. FLT_MAX_10_EXP or DBL_MAX_10_EXP or LDBL_MAX_10_EXP: Maximum integer value for the exponent of a base-10 expression that would generate a normalized floating-point number.
Minimum value is 37
10. FLT_MAX or DBL_MAX or LDBL_MAX: Maximum finite representable floating-point number.
Minimum value is 1037
11. FLT_EPSILON: Difference between 1 and the least value greater than 1 that is representable.
Maximum value is 10-5
12. DBL_EPSILON or LDBL_EPSILON: Difference between 1 and the least value greater than 1 that is representable.
Maximum value is 10-9
13. FLT_MIN or DBL_MIN or LDBL_MIN: Minimum representable positive floating-point number.
Maximum value is 10-37
14. FLT_ROUNDS: Rounds off the floating-point number Different possible values are:
- -1 : indeterminate
- 0 : towards zero
- 1 : towards one
- 2 : towards positive infinity
- 3 : towards negative infinity
15. FLT_EVAL_METHOD: Rounds off the floating-point number Different possible values are:
- -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 and Other
- negative values indicate an
- implementation defined behavior.
Below is the program to demonstrate the working of macros constants in cfloat library.
// C++ program to demonstrate working
// of macros constants in cfloat library
#include <cfloat>
#include <iostream>
using namespace std;
int main()
{
cout << "FLT_RADIX : "
<< FLT_RADIX << endl;
cout << "FLT_DIG : "
<< FLT_DIG << endl;
cout << "DECIMAL_DIG : "
<< DECIMAL_DIG << endl;
cout << "FLT_MIN_10_EXP : "
<< FLT_MIN_10_EXP << endl;
cout << "FLT_MAX_EXP : "
<< FLT_MAX_EXP << endl;
cout << "FLT_MAX_10_EXP : "
<< FLT_MAX_10_EXP << endl;
cout << "FLT_MAX : "
<< FLT_MAX << endl;
cout << "FLT_MIN : "
<< FLT_MIN << endl;
return 0;
}
Output
FLT_RADIX : 2 FLT_DIG : 6 DECIMAL_DIG : 21 FLT_MIN_10_EXP : -37 FLT_MAX_EXP : 128 FLT_MAX_10_EXP : 38 FLT_MAX : 3.40282e+38 FLT_MIN : 1.17549e-38
