Boolean keywords and system routines

[fawltyl...@gmail.com]

Hi all,

most of the system routines are compiled C functions, but there are some routines distributed as .pro source file in the IDL lib directory. Source files use KEYWORD_SET() to evaluate boolean keywords, with well documented rules. However,  the builtin C routines use different rules,:

IDL> help, keyword_set(0.5)
<Expression>    INT       =        1

IDL> help, where(0, null=0.5)
<Expression>    LONG      =           -1

0.5 is true in the first case, false in the second. For non-integer keywords, users must know the type of the system routine to use it correctly. Is this a bug or a feature?

best regards,

Lajos

(this was originally discovered by the GDL folks.)

[Chris]

Hey Lajos,

I don't know if this is really a bug, but it's definitely a difference between PRO code and C code. In the C code, it always converts the input keywords to the desired IDL data type. In this case, "on/off" keywords are always converted to the LONG type, which just returns 0, which of course is then "off" for the keyword.

As I'm sure you know, it's way too late to change any of this behavior. :-)

Cheers,

Chris

NV5 Geospatial Software