Trigger programming..

I have a function written in C, a trigger calls this function on the table
applicants. I need to get the value from a field named "app_id" in the table
that the trigger is pulled on (applicants)..

I have this code...

app_id_fieldname is a character pointer with value "app_id". char_app_id is
always NULL though.. I'm totally guessing at most of this from looking
through some examples and the SPI section of the programmer's manual.

Someone school me -- please! :-)

tupdesc = rel->rd_att; /* what the tuple looks like (?) */

app_id_colnum = SPI_fnumber(tupdesc, app_id_fieldname);

if (app_id_colnum == SPI_ERROR_NOATTRIBUTE)
elog(ERROR, "app_id_colnum - SPI_ERROR_NOATTRIBUTE error ");

char_app_id = SPI_getvalue(rettuple, tupdesc, app_id_colnum);

Thanks!!

-Mitch