>>>>>Cetin and Ed:
>>>>>
>>>>>With your help now this code is working. But sometimes DoubleToNum function provokes C000005 error.
>>>>>
>>>>>Indeed I am forgetting something.
>>>>>
>>>>>Alejandro Fernandez
>>>>Alejandro,
>>>>Are you sure it's DoubleToNum invoking C000005 ? Might it something else with DLL.
>>>>Cetin
>>>
>>>I found this error tracing the source with SET STEP ON.
>>
>>That will happen if the address in memory is not valid; either it's non-existant, or you do not have read privileges for the address. Check the value of the pointer - some people's implementation of the DWORDToNum() UDF is subtly flawed, since VFP treats a 4 byte integer as a value between -2147483647 to 2147483647, not 0 to 4294967295.
>
>C000005 error appear sometimes when and UDF is called too. It's not always in DoubleToNum function. Sometimes calling my DLL provokes the same error.

It's a memory management error of some sort - if you're using VFP 6, ensure that you've upgraded to at least SP3, and preferably to SP6 or later. AFA UDFs, the functions included in ClsHeap are well-behaved, and do proper casting of elements, so if you've rolled your own, investigate using the ones in the current public release of ClsHeap, available on UT or my web site.

>
>I had thought to check pointer in order to avoid it, but I don`t know exactly what function to use here.
>

Depending on what the pointer is being used for (read/write/execute) there are a whole series of pointer validation APIs; see the MSDN Platform SDK docs.