User hook for command SET VARIABLE USER

If CLASS knows about a User Subsection owner and title when SET VARIABLE USER is invoked, it can instantiate the SIC variables which describe the data of this subsection. This is be done if the associated hook has been defined and declared to CLASS. The steps to do so are, as usual:

1. tell CLASS which subsection it owns with class_user_owner. This is optional if it has been done elsewhere.
2. declare to CLASS with class_user_setvar a subroutine which is able to instantiate the SIC variables associated to the User Subsection.

The subroutines class_user_def_inte, class_user_def_real and class_user_def_dble and class_user_def_char will create respectively an integer*4, real*4 and real*8 and character string in R%USER%OWNER% (where OWNER is the owner previously declared). The subroutines order must match the order the data was written in the User Section buffer.

The calling sequence of these subroutines is described in the following sections. The suffix name of the SIC variable is given as first argument, e.g. FOO for R%USER%OWNER%FOO. The arguments 'ndim' and 'dims' describe the variable dimensions, but only scalars and 1D-arrays are currently supported (ndim=0 or 1). For the character variables, 'strlen' is the string length which has to be read from the buffer.

Note that once it has been instantiated, the SIC structure R%USER%OWNER% will be updated each time the data changes (e.g. after a GET NEXT).