Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Thu, 13 Dec 2012 15:05:40 -0600

Hi Dehong,

On 2012-12-13 Zhang, Dehong wrote:
> 
> I am writing a custom record to deal with a particular hardware.  This
> hardware has a few different operation modes, which are represented
> with a set of name strings, not numbers.  We can talk to it to get or set
> this mode, with strings.
> 
> The problem is, when a choice is made, we get a menu choice number.
> Then I will need to find the corresponding name string, to write to the
> hardware; on the other direction, when I query the hardware to find its
> current mode, I get back a string.  Then I need to find the corresponding
> choice number to set the button properly.
> 
> All these name strings are defined in the menu definition.  How can I
> access them inside the record support?  Without having to declare
> an array of strings, beside the menu definition?

dbStaticLib.h defines the function
    dbMenu* dbFindMenu(DBBASE *pdbbase, const char *name);

The dbMenu structure is defined in dbBase.h which gets included by 
dbStaticLib.h anyway.

So to access the choice strings you could use a function like this:

const char * menuChoice(const char *menuName, epicsEnum16 index)
{
    dbMenu pMenu = dbFindMenu(pdbbase, menuName);
    if (!pMenu || index >= pMenu->nChoice)
        return NULL;

    return pMenu->papChoiceName[index];
}

Note that dbFindMenu() uses a hash table which is reasonably fast, but you 
might still want to do the lookup just once at initialization and save the 
dbMenu pointers for all your menus.

The disadvantage of making your menu choices identical to the strings that you 
use to communicate with the device is that you can't change their wording to 
make them easier for your users to understand.  I would think carefully about 
that before using the above code, although there's nothing inherently wrong 
with using this approach if that's acceptable.

HTH,

- Andrew
-- 
Computer science is as much about computers as astronomy is about
telescopes. -- Edsger Dijkstra

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System