Download HALCON Programmer`s Guide

282
General Information
30.2
Tips and Tricks
30.2.1
Troubleshooting
?
Executed program or procedure raises exception for display operators like set_tposition
when not using implementation of display operators
If you are not using an implementation of HDevelop’s internal display operators (dev_*), calls
to these operators in the executed HDevelop program or procedure are simply ignored. However,
if the program or procedure contains other, “external” display operators like set_tposition or
write_string, which need a window handle as input parameter, the program / procedure will
raise an exception at this operator if the window handle has not been instantiated.
Typically, this problem will not arise when executing programs, because you will in most cases
use an implementation of the display operators. When executing procedures, we recommend to
leave out the external display operators that use window handles. If this is not possible, you
could place them in a separate procedure and use the implementation of display operators for just
this procedure. Alternatively, initialize the window handle with a value like -1 and test it before
executing the external display operators.
?
External procedures cannot call local procedures
Note that local procedures can call external procedures but not the other way round.
30.2.2
Loading and Unloading Procedures
In most applications there is no need to delete loaded HDevelop procedures explicitly using
UnloadProcedure. A reason might be to free memory.
Please note that when creating a procedure with the class HDevProcedure, the procedure is loaded
together with all the procedures it uses. In contrast, UnloadProcedure deletes only the specified procedure. To delete the automatically loaded procedures, you can query their names using
GetLoadedProcedureNames and then delete them (if you are sure that they are not used by another
loaded procedure!), or you can use UnloadAllProcedures to unload all external procedures.
As an alternative, you can reset the external procedure paths by passing an empty string to
SetProcedurePath or call UnloadAllProcedures.