ctypes - pointer to array of structs?

[skip@pobox.com]

(Is this the right place to ask ctypes questions? There's a mailing list
but the last post to it seems to have been in November 2006.)

Using ctypes I reference a structure which contains a pointer to an array of
another structure:

class SYMBOL(Structur e):
_fields_ = [("symbol", c_char_p),
("num", c_int),
("units", c_int),
("baseprice" , c_int),
("active", c_int)]
SYMBOL_PTR = POINTER(SYMBOL)

class TABLE(Structure ):
_fields_ = [("map", SYMBOL_PTR),
("nsymbols", c_uint),
...]

Effectively, TABLE.map is an array of TABLE.nsymbols SYMBOLS. How to I
reference elements in that array? In C I would just treat TABLE.map like an
array and index into it (for i=0; i< TABLE.nsymbols; i++) ...). This is
data returned from a C library, not something I'm building in Python to pass
into C.

Thx,

Skip

[Diez B. Roggisch]

Re: ctypes - pointer to array of structs?

skip@pobox.com schrieb:

(Is this the right place to ask ctypes questions? There's a mailing list
but the last post to it seems to have been in November 2006.)

No, it's active.

Using ctypes I reference a structure which contains a pointer to an array of
another structure:
>
class SYMBOL(Structur e):
_fields_ = [("symbol", c_char_p),
("num", c_int),
("units", c_int),
("baseprice" , c_int),
("active", c_int)]
SYMBOL_PTR = POINTER(SYMBOL)
>
class TABLE(Structure ):
_fields_ = [("map", SYMBOL_PTR),
("nsymbols", c_uint),
...]
>
Effectively, TABLE.map is an array of TABLE.nsymbols SYMBOLS. How to I
reference elements in that array? In C I would just treat TABLE.map like an
array and index into it (for i=0; i< TABLE.nsymbols; i++) ...). This is
data returned from a C library, not something I'm building in Python to pass
into C.

I think you should be able to create an array-type with the required
number of entries, and cast map to that. Along these lines (untested)

ap = POINTER(SYMBOL( table.nsymbols) )

map = cast(table.map, ap)

Diez

[Skip Montanaro]

Re: ctypes - pointer to array of structs?

(Is this the right place to ask ctypes questions? There's a mailing list

but the last post to it seems to have been in November 2006.)

>
No, it's active.

Thanks. I guess the official ASPN-based archive must be dead.

I managed to sort of get access to the array just using indexing
as I would in C, but I'm having some problems referencing
elements of the SYMBOL struct. I'll keep plugging away.

Skip