Re: [Vala] vala-list Digest, Vol 133, Issue 6

[Vivien Kraus <vivien planete-kraus eu>]

Hi,

Thank you for your answer.  In fact, the_datum is a plain int.  So it cannot be NULL (error: Equality 
operation: `null'
and `int' are incompatible).

However, I found a workaround.  It seems that valac assumes out parameter to extern library functions are 
always
initialized, but not when they are called conditionally.

So, by changing a little the code, I got this to compile:

// Always return true
extern bool lib_initialized ();

// data is always set when work returns true
extern bool lib_work (out int data);

int main(string[] args) {
        int the_datum;
        if (lib_initialized ()) {
                bool has_datum = lib_work (out the_datum);
                if (has_datum) {
                        stdout.printf ("Hello, %d!\n", the_datum);
                }
        }
        return 0;
}

Le samedi 16 février 2019 à 12:52 -0200, Fernando Silva via vala-list a écrit :
> I think checking if (the_datum != null) should do
>
> Em sáb, 16 de fev de 2019 10:00, <vala-list-request gnome org escreveu:
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> >    1. error: use of possibly unassigned local variable (Vivien Kraus)
> >
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> > ----------------------------------------------------------------------
> >
> > Message: 1
> > Date: Fri, 15 Feb 2019 21:28:45 +0100
> > From: Vivien Kraus <vivien planete-kraus eu>
> > To: vala-list gnome org
> > Subject: [Vala] error: use of possibly unassigned local variable
> > Message-ID:
> >         <40a1141df0d06b59ed0f87f3a6cafac285f45b4a camel planete-kraus eu>
> > Content-Type: text/plain; charset="UTF-8"
> >
> > Hello list,
> >
> > I am facing an inconvenient problem.
> >
> > Suppose I have a C library, that I want to use from vala:
> >
> > // Always return true
> > extern bool lib_initialized ();
> >
> > // data is always set when work returns true
> > extern bool lib_work (out int data);
> >
> > int main(string[] args) {
> >         int the_datum;
> >         bool has_datum = (lib_initialized () && lib_work (out the_datum));
> >         if (has_datum) {
> >                 stdout.printf ("Hello, %d!\n", the_datum);
> >         }
> >         return 0;
> > }
> >
> > If I am to compile this (0.42.5, -C only, not link), I get an error
> > message:
> >
> > test.vala:11.3-11.44: error: use of possibly unassigned local variable
> > `the_datum'
> >                 stdout.printf ("Hello, %d!\n", the_datum);
> >                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > Compilation failed: 1 error(s), 0 warning(s)
> >
> > The workaround is obvious: initialize the_datum.  However, I like to run
> > my code under valgrind to detect when reading
> > from an uninitialized variable (I make lots of mistakes ^^), and so if
> > there is a bug in lib_work and I initialize
> > the_datum, then I will not be able to notice the problem.
> >
> > Is it possible to instruct valac that it should not worry?  Or is it
> > possible to change this error to a simple warning?
> >
> > Best regards
> >
> > Vivien
> >
> >
> >
> >
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> > End of vala-list Digest, Vol 133, Issue 6
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