[Cuis-dev] FFI example

[Vanessa Freudenberg]

For one, there's no reason to subclass ExternalLibrary.

But otherwise, it works for me:

[image: image.png]

[image: image.png]

That said, if you actually want to use C functions in your application, the
better way is to build a VM plugin. It's a little bit more overhead to
learn but fits the Smalltalk philosophy much better, where the VM provides
the environment for the image to live in, rather than the image talking to
the outside world directly. The job of the VM is to provide a safe world
so Smalltalk developers don't have to worry about the harsh reality. FFI
breaks that illusion.

Vanessa

On Mon, Sep 30, 2024 at 8:10 AM Mark Volkmann via Cuis-dev <
cuis-dev at lists.cuis.st> wrote:

> Vanessa's getenv example works for me. Now I want to learn how to invoke
> my own C functions.
> I created the file "mylib.c" containing this:
>
> char* greet() {
>   return "Hello, World!";
> }
>
> Then I created a shared library for macOS with this:
>
> clang -dynamiclib -o libmylib.dylib mylib.c
>
> Then I created this Smalltalk class:
>
> ExternalLibrary subclass: #FFIDemo
>     instanceVariableNames: ''
>     classVariableNames: ''
>     poolDictionaries: ''
>     category: 'Volkmann'
>
> Then I added this class method:
>
> greet
>     <cdecl: char* 'greet' () module:
> '/Users/volkmannm/Documents/dev/lang/smalltalk/Cuis-Smalltalk-Volkmann/libmylib.dylib'>
>     ^self externalCallFailed
>
> Side note: I need to learn where this looks by default for shared
> libraries so I don't have to specify an absolute path.
>
> Then I entered this in a Workspace and did a "Print it".
>
> FFIDemo greet
>
> That opens a Debug window with the message "Error: Unable to find function
> address".
>
> Can anyone spot where I'm going wrong?
>
> On Sun, Sep 29, 2024 at 10:10 PM Andres Valloud via Cuis-dev <
> cuis-dev at lists.cuis.st> wrote:
>
>> Except of course getenv() is ruled by POSIX so doing that is at the very
>> least not portable, if not outright wrong.
>>
>> On 9/29/24 6:29 PM, Vanessa Freudenberg via Cuis-dev wrote:
>> > And, defining a method myself works fine:
>> >
>> > getenv: var
>> >          <cdecl: char* 'getenv' (char*) module: 'libSystem.dylib'>
>> >          ^self externalCallFailed
>> >
>> > And then
>> >
>> >     MyClass getenv: 'HOME'
>> >
>> >
>> > returns
>> >
>> >       '/Users/vanessa' .
>> >
>> >
>> > There really isn't much more to it.
>> >
>> > Vanessa
>> >
>> > On Sun, Sep 29, 2024 at 6:26 PM Vanessa Freudenberg
>> > <vanessa at codefrau.net <mailto:vanessa at codefrau.net>> wrote:
>> >
>> >     I just loaded the "Tests-FFI" package and it works.
>> >
>> >     And you can e.g. run
>> >
>> >           FFITestLibrary new ffiTestFloats: 3 with: 4
>> >
>> >     which returns 7.0 because the plugin happens to implement
>> >     "ffiTestFloats()" as returning the sum of its two arguments.
>> >
>> >     Vanessa
>> >
>> >
>>
>> --
>> Cuis-dev mailing list
>> Cuis-dev at lists.cuis.st
>> https://lists.cuis.st/mailman/listinfo/cuis-dev
>>
>
>
> --
> R. Mark Volkmann
> Object Computing, Inc.
> --
> Cuis-dev mailing list
> Cuis-dev at lists.cuis.st
> https://lists.cuis.st/mailman/listinfo/cuis-dev
>
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