Floating-point types

Floating-point type specifiers fall into the following categories:

Real floating-point types
Complex floating-point types

Real floating-point types

Generic, or binary, floating-point types consist of the following:

float
double
long double

Decimal floating-point types consist of the following:

_Decimal32
_Decimal64
_Decimal128

Note: In order for the _Decimal32, _Decimal64, and _Decimal128 keywords to be recognized, you must compile with the -qdfp compiler option. See -qdfp for details.

The magnitude ranges of the real floating-point types are given in the following table.

Table 1. Magnitude ranges of real floating-point types
Type	Range
float	approximately 1.2^-38 to 3.4³⁸
double, long double	approximately 2.2^-308 to 1.8³⁰⁸
_Decimal32	0.000001^-95 to 9.999999⁹⁶
_Decimal64	0.000000000000001^-383 to 9.999999999999999³⁸⁴
_Decimal128	0.000000000000000000000000000000001^-6143 to 9.999999999999999999999999999999999⁶¹⁴⁴

If a floating-point constant is too large or too small, the result is undefined by the language.

The declarator for a simple floating-point declaration is an identifier. Initialize a simple floating-point variable with a float constant or with a variable or expression that evaluates to an integer or floating-point number.

You can use decimal floating-point types with any of the operators that are supported for binary floating-point types. However, you cannot mix decimal floating-point types with generic floating-point types or complex floating-point types in arithmetic expressions unless you use explicit conversions. Implicit conversions are applicable as follows:

Implicit conversions among decimal floating-point types are always supported.
Implicit conversions between decimal floating-point types and integral types are always supported.
Implicit conversions between decimal floating-point types and generic floating-point types are supported conditionally. See Floating-point conversions for details.

Complex floating-point types

Complex floating-point types are introduced in the C99 standard. C++ only

The XL C/C++ compiler supports this feature as an IBM extension. C++ only

The complex floating-point type specifiers are as follows:

float _Complex
double _Complex
long double _Complex

The representation and alignment requirements of a complex type are the same as an array type containing two elements of the corresponding real type. The real part is equal to the first element; the imaginary part is equal to the second element.

The equality and inequality operators have the same behavior as for real types. None of the relational operators may have a complex type as an operand.

IBM extension As an extension to C99 and C++03, complex numbers may also be operands to the unary operators ++ (increment), -- (decrement), and ~ (bitwise negation).

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