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Using and Porting GNU Fortran

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8.7.2 Constants

(Corresponds to Section 4.2 of ANSI X3.9-1978 FORTRAN 77.)

A typeless constant has one of the following forms:

 
'binary-digits'B
'octal-digits'O
'hexadecimal-digits'Z
'hexadecimal-digits'X

binary-digits, octal-digits, and hexadecimal-digits are nonempty strings of characters in the set `01', `01234567', and `0123456789ABCDEFabcdef', respectively. (The value for `A' (and `a') is 10, for `B' and `b' is 11, and so on.)

A prefix-radix constant, such as `Z'ABCD'', can optionally be treated as typeless. See section Options Controlling Fortran Dialect, for information on the `-ftypeless-boz' option.

Typeless constants have values that depend on the context in which they are used.

All other constants, called typed constants, are interpreted--converted to internal form--according to their inherent type. Thus, context is never a determining factor for the type, and hence the interpretation, of a typed constant. (All constants in the ANSI FORTRAN 77 language are typed constants.)

For example, `1' is always type INTEGER(KIND=1) in GNU Fortran (called default INTEGER in Fortran 90), `9.435784839284958' is always type REAL(KIND=1) (even if the additional precision specified is lost, and even when used in a REAL(KIND=2) context), `1E0' is always type REAL(KIND=2), and `1D0' is always type REAL(KIND=2).


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