[PD-dev] string type for pd

[Martin Peach]

Thomas Grill wrote:
> Hi Martin,
> many thanks for your initiative, it is greatly appreciated!
> It would be extremely useful to also define some API for string 
> handling right from the start, to be able to use the string type in 
> externals... all those functionality that seems to be contained in 
> your str object.
>
:)
Part of the patch adds lines to m_pd.h to give a basic API:

A t_string is defined:
typedef struct _string /* pointer to a string */
{
   unsigned long s_length; /* length of string in bytes */
   unsigned char *s_data; /* pointer to 1st byte of string */
} t_string;

...and a w_string is added to t_word:

    t_string *w_string;
 } t_word;
 
t_atomtype is extended with A_STRING:
    A_STRING
 }  t_atomtype;

and the public functions are prototyped: 
EXTERN t_symbol s_string;
#define SETSTRING(atom, st) ((atom)->a_type = A_STRING, (atom)->a_w.w_string = (st))
EXTERN t_string *atom_getstring(t_atom *a);
EXTERN void pd_string(t_pd *x, t_string *st);
EXTERN void outlet_string(t_outlet *x, t_string *st);
EXTERN void class_addstring(t_class *c, t_method fn);
#define class_addstring(x, y) class_addstring((x), (t_method)(y))

The [str] object contains the other functions, you can see them in str.c in /externals/mrpeach/str.
Should they be public? I was thinking of an object like [list] which has selectors for various functions.
Of course, any external can use t_strings once they are supported by pd.
Some other issues are lying around, such as what is the largest possible string.
I used MAXPDSTRING but I think that there should be no limit -- string objects should be ready to handle strings that are longer than they have memory for, without crashing.
In the str object the s_length field holds the available memory and a separate private field holds the current length, but when passed as an atom through an outlet, s_length contains the true length of the string.

Martin