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TRUE
Boolean data type
#include <Types.h>
typedef enum { /* ie, enumerated 16-bit integer */
false = 0,
true = 1,
FALSE = 0,
TRUE = 1
} Boolean;
Notes: As an enumerated C-language data type, a Boolean is simply a 16-bit short
containing either 0 or 1. In a statement such as:
if ( foo ) { doit... }
'doit' will be executed in all cases except when 'foo' is exactly zero. Thus,
you can use a short instead of a Boolean.
The Pascal storage of a 'Boolean' data type is somewhat different - and the
difference can be important. Pascal, and thus the Macintosh toolbox,
considers a BOOLEAN to be exactly 1 bit long; for instance, a PACKED array
of 16 BOOLEANs will fit into a 16-bit word (as in GetKeys). When a
BOOLEAN toolbox function returns 'true', the actual value is 256 (bit 0 of
the high byte is set).
Your compiler's glue library is nice enough to fetch that byte off the stack
and extend it into a 16-bit integer. When calling the toolbox, the compiler
also takes care of storing non-zero values into the high byte of any BOOLEAN
parameter. But there are still two places where this might cause a
problem:
• When you create a 'callback' routine, such as a file filter
(SFGetFile) or an event pre-processing filter (ModalDialog),
you are expected to return a BOOLEAN to the system. In that case, you
must NOT return an integer 1. As long as you correctly declare your
routine as a "pascal Boolean", you will never have a problem.
• When accessing global variables listed as BOOLEAN, be sure to check
the first byte at the global address. 0 means false, else means true.
In some cases, a value of 0xFF is used to indicate true.
Referenced by (621):