Re: Receive a pointer to a struct from an external function ?

[gbWilly <gbWilly@xxxxxxxxxxxxxx>]

On Sunday, February 15th, 2026 at 22:34, Benoît Minisini <benoit.minisini@xxxxxxxxxxxxxxxx> wrote:

> Le 15/02/2026 à 22:10, Lee a écrit :
> > While working with Libc, I encountered an issue when receiving a pointer
> > to a structure from an external function.
> >
> > The C structure contains members which are declared as "char *". I
> > declared the Gambas structure with those members "As String". But,
> > attempting to print the string values causes a Segmentation Fault.
> >
> > If those very members are declared "As Pointer", using String@ to print
> > the values works.
> >
> > Is this a bug in the external interface, an unrealistic expectation on
> > my part, or something I am doing incorrectly?
> >
> > Project attached.
> >
> >
> 
> Inside a Gambas structure, a String is a Gambas string, and only Gambas
> can create it. So if you use it to store a C string (a 'char *'), you
> need to use a Pointer.
> 
> It's only for function argument and function return value that you can
> use the Gambas String datatype, provided that you use it correctly as
> explained in the wiki.
> 
> In other words, you really need to know how C works to understand what
> you can do, and how you can do it in all cases.
> 
> Regards,
> 
> --
> Benoît Minisini.
> 

This confirms what I encountered.
First I used the String and Integer data types in my Struct and it didn't work.
Changing all to Pointers and using String@ and Integer@ to show the data did work.

Good to know it is different that the arguments.

Thanks you for the clear explanation.

gbWilly

GambOS
Gambas3 for Debian/Ubuntu

...there is always a Catch if things go wrong!