NAME

DoCallback − Create a callback object

SYNOPSIS

C:

DtObject DoCallback(function,dataobject)
DtPtr function;
DtObject dataobject;

FORTRAN:

INTEGER∗4 DOCB(SUBPGM,DATOBJ)
EXTERNAL SUBPGM
INTEGER∗4 DATOBJ

DESCRIPTION

DoCallback creates a callback object.  The function parameter is a pointer to a user-defined function.  The dataobject parameter is the handle of an object containing the associated run-time data for the user-defined function.  This parameter is created with either DoDataPtr <DODP> or DoDataVal <DODV>.  DoCallback calls function with the run-time data of dataobject.  Set dataobject to DcNullObject <DCNULL> when the user-defined function requires no data. 

The format for the user-defined function in C is:

 user_fcn(data)
DtPtr data;           /∗ if DoDataPtr was used ∗/
Dt32Bits data;        /∗ if DoDataVal was used ∗/

FORTRAN, the user-defined function can be either a subroutine or a function. The format is either:

 SUBROUTINE SUBPGM(DATA)
INTEGER∗4 DATA
 

or

 FUNCTION SUBPGM(DATA)
INTEGER∗4 DATA
 

Note that sometimes rendering methods involve multiple traversals of the Doré database, which means an update will cause callback objects and their user-written functions to be executed multiple times. 

ERRORS

DoCallback will fail if dataobject is neither an object created with DoDataVal <DODV> or DoDataPtr <DODP> nor DcNullObject <DCNULL>. 

[WARNING - invalid dataobject handle]

SEE ALSO

DdInqPickCallback(3D), DdSetPickCallback(3D), DoDataPtr(3D), DoDataVal(3D), DsExecuteObj(3D), DsExecutionAbort(3D), DsExecutionReturn(3D)

September 02, 1992