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

Thanks for the fast answer. :-) On 30/05/16 11:14, Esteban Lorenzano wrote:

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 :) I think I will use the second solution. It is cleaner isn't it?

Julien