more custom C function fun

I have a custom C function that takes two text*s and returns a text*.

My problem is with this code:


PG_FUNCTION_INFO_V1(get_agent);

PGMODULEEX****T Datum get_agent(PG_FUNCTION_ARGS)
{
	if(!PG_ARGISNULL(0))
	{
		text* calling_party = PG_GETARG_TEXT_P(0);

		char* thestr = VARDATA(calling_party);
		if(thestr[20] == ')')
		{
			PG_RETURN_TEXT_P(calling_party);
		}
	}
/* the other argument is ignored for now */
	PG_RETURN_NULL();
}

The problem is, the comparison in the inner if statement is always true. 
  If I change to compare, say, thestr[0] == 'N', then it works as 
expected (returning only those text*s whose first letter is N, returning 
null for the rest).

However if I try to compare any character inside the text* with a 
parenthesis (both '(' and ')'), then the equality is apparently always 
true (the function never returns null, always returning calling_party), 
whether or not there is any data in that column that contains a 
parenthesis in that column.

Does anyone know of any oddities or whatnot I should be accounting for 
when reading character data out of a text*?

- Dan

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