FFI structs

I I have a C struct with a char*

struct result {
        char* time }

I define an ExternalStructure in FFI , with one field of type char* (note that the syntax char [5] is not accepted ! ).

defineFields generates the accessors time and time:

If I use
time: ’05:45’

I get an error.
How do I set a string value in an ExternalStructure ?

Annick

On 29.10.2014, at 06:59, Annick Fron <[hidden email]> wrote:
Just like in C. You need to create a pointer to a char array and store that. Which means you need to allocate some bytes (ExternalAddress allocate: byteSize + 1), copy your string there (byteAt:put:), add a terminating 0 byte, then store the address of that in your struct. Be sure to free the memory allocated when you're done.

I think there used to be a helper function for that but I can't find it (only found fromCString).

- Bert -

Hi Annick,

you can't pass smalltalk strings or objects to ffi as parameters,
you have to allocate the buffer member of your structure
on the external heap ( plus to avoid being gc'd before ffi call)
with ExternalAddress allocate: <your buffer/string size +1 for string
null termination>
fill your buffer with byteAt:put: method,
and release this memory with free when you have finished.

not sure, but you could try something like:

s := '05:45' copyWith: (Character value: 0).
a := ExternalAddress allocate: s size.
s asByteArray withIndexDo: [ :b :i | a byteAt: i put: b  ].
myStruct time: a.
... call your ffi ...
a free


Regards,

Alain

Le 29/10/2014 11:59, Annick Fron a écrit :