[Rd] Problem with types on 64-bit

[tom at levelelimited.com]

Hi Everyone,

I have a problem using some working 32-bit R code with 64-bit machine ( I am
using version R-2.4.1 ).  The problem occurs when I am trying to detect a NULL
STRSXP type. ( Perhaps I am doing this detection in the wrong way? )

On 32-bit the following works, and correctly identifies if I am passing NULL
or a valid string object:

if ( v_dta_start != R_NilValue && STRING_ELT( v_dta_start, 0 ) != R_NilValue )
{
    dta.start = CHAR( STRING_ELT( v_dta_start, 0 ) );
}

Yet on a 64-bit machine I get the following errors:

(1) when I pass NULL it goes into the if clause and then when it tries to set
dta.start it displays:
CHAR() can only be applied to a 'CHARSXP', not a 'NULL'
(2) if I pass a valid string such as "hello", I get the following:
CHAR() can only be applied to a 'CHARSXP', not a 'character'

I have tried converting using AS_CHARACTER but that just brings up the same
messages.  I have also seen S4 and PROMSXP types come up in these error
messages.  

What I don't understand is why this happens - any ideas?

If I can supply any more info let me know, below is the CPU information for
the 64-bit machine. 

Many thanks for your help

Tom

64-BIT CPU INFO
===============

processor	: 0
vendor_id	: AuthenticAMD
cpu family	: 15
model		: 5
model name	: AMD Opteron(tm) Processor 144
stepping	: 10
cpu MHz		: 1794.932
cache size	: 1024 KB
fpu		: yes
fpu_exception	: yes
cpuid level	: 1
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat
pse36 clflush mmx fxsr sse sse2 syscall nx mmxext lm 3dnowext 3dnow
bogomips	: 3597.08
TLB size	: 1024 4K pages
clflush size	: 64
cache_alignment	: 64
address sizes	: 40 bits physical, 48 bits virtual
power management: ts fid vid ttp