[PD] external: method to convert t_atom to c string.

[Jonathan Wilkes]

On 05/19/2013 11:47 PM, J Oliver wrote:
> Hello all,
>
> I need to create a textfile from inside an external and I need to give 
> the computer a path with a message like:
>
> path /home/path/file.txt
>
> I am therefore creating a method for path with:
>
> class_addmethod(testtext_class, (t_method)testtext_path, 
> gensym("path"), A_GIMME, 0);
>
> Or should I use A_DEFSYMBOL ?

I'd use A_DEFSYMBOL if you want the user to be able to send a "path" 
message with no args,
and A_SYMBOL if you want to require them to specify some path.

>
> But then how can I read the atom inside the external?
>
> I am using:
>
> void testtext_path(t_testtext *x, t_atom *s){
> char teststring[1000];
> atom_string(s, teststring, 1000);
> post(teststring);
> }
>
> but then I get the following printout:
>
> consistency check failed: atom_string
> 333333@ÿÿÿÿs
>
> I'm not sure where to move with this. anybody has any suggestions?

I don't have time to check it but I'd imagine the problem is that 
A_GIMME assumes the method wants the following args: t_testtext*, 
t_symbol*, int, and a t_atom*

where the t_symbol* refers to the selector that was used to call the 
method-- in this case, the word "path".  (That can come in handy, btw, 
as you can have methods "chocolate" and "vanilla" point to the same 
foo_icecream function and branch based on which selector was used.)

However, you only specified two arguments for that method, and one of 
them is t_atom* so I guess it implicitly casts from the t_symbol* it 
receives.  (I think the compiler warns you about stuff like this but I'm 
no expert so maybe I'm wrong.)

Then inside atom_string (in m_atom.c) it switches based on a->a_type, 
but your "a" doesn't have an a_type because it's really a t_symbol*.  
Thus none of the cases match and so the function ends up calling the 
"bug" function that prints out the error you see.

Essentially you tried to build a string using a reference to an atom 
that's not really an atom, so Pd complained that you weren't being 
consistent.

-Jonathan

>
> best,
>
> J
>
> Here's the info for atom_string:
>
>
>       atom_string
>
> void atom_string(t_atom *a, char *buf, unsigned int bufsize);
> Converts an atom |a| into a C-string |buf|. The memory to this 
> char-Buffer has to be reserved manually and its length has to be 
> declared in |bufsize|.
>
> in: 
> http://pdstatic.iem.at/externals-HOWTO/node9.html#SECTION00092200000000000000
>
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