Re: how to determine record type given pointer to a record

[Andrew Johnson <anj@aps.anl.gov>]

John Dobbins wrote:
> I'm writing a bit of code that has to deal with multiple record types 
> but is only passed a pointer to the record. What is the easiest way to 
> determine the record type (or even just dset type)?
>
> e.g. since I don't the record type I'm being passed I first cast the 
> pointer as (dbCommon *), then precord->rdes->name will give me the 
> record type name as a string which I can compare to say "ai"
>
> but is there a simpler way?

If this is for a device support layer that you're writing and you know 
that you've already initialized the record, you could arrange to have an 
enum or other marker in the structure that the DTYP field points to.

Here's the start of the definition of a dpvt structure that I use in my 
directNetAsyn support; the enum recType field is how I decide which 
record type this particular record belongs to:

struct dpvtIn {
    struct dbCommon *precord;
    enum recType {AI, AIF, BI, MBBI, MBBID} type;
    ...
};

In my device support's init_record routine I allocate a dpvtIn structure 
and point to it from the DPVT field, making sure that I initialize the 
dpvt->type field to the appropriate value.


However if this is more general-purpose and could be any record, your 
rdes->name may be the best way to determine the type.  It really depends 
what you want to do with the result.

- Andrew
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* * Matt Santos / / For a Brighter America * *