Re: [Pharo-users] Unified FFI: pointer of String as function parameter

this is not the easiest part of FFI :) this is the simplest way: str := ExternalAddress new. “This will point to NULL” self callToMyFunction: str. pharoString := (str pointerAt: 1) readString. callToMyFunction: str self ffiCall: #( void function ( char ** str ) ) now, another way is to declare a value holder: 1) subclass FFIExternalValueHolder. FFIExternalValueHolder subclass: #StringValueHolder. 2) implement class side method typeDesc StringValueHolder class>>typeDesc ^ String 3) implement your method replacing char** for your value holder: callToMyFunction: str self ffiCall: #( void function ( StringValueHolder* str ) ) then you call like this: str := StringValueHolder new. self callToMyFunction: str. pharoString := str value readString. looks like too much steps for just economise the “pointeAt: 1” part, but is useful when you have lots of this calls :) cheers, Esteban

On 30 May 2016, at 10:56, Julien Delplanque <julien@tamere.eu> wrote:

Hello everyone,

I have a C function to call from Pharo that looks like this:

int my_function(char ** parameter);

This function fill the pointer on the String given as parameter.

How can I use this from pharo Unified FFI? I mean, how to get a pharo String filled by this function?

Thanks in advance,

Julien