Working with ctypes and char** data type

[Philluminati]

I'm a bit of a python newbie and I need to wrap a C library.

I can initialise the library using CDLL('mcclient. so')

and I can call functions correctly inside the library but I need to
invoke one function which has this function definition:

char ** CAPAPI McSearch(HMCLIN K Handle,
short nSearchType,
short nNoSelect,
char **pSelect,
short nNoWhere,
char **pWhere,
char **pData,
int iTimeout);

For **pSelect I want to pass in an array of char points, which in C
would be declared as

char *pData[] = { "ADDR", "POSTCODE" };

Can someone tell me how use pointers + char pointers together in
python with ctypes please?

Thank you

Phill

[Thomas Heller]

Re: Working with ctypes and char** data type

Philluminati schrieb:

I'm a bit of a python newbie and I need to wrap a C library.
>
I can initialise the library using CDLL('mcclient. so')
>
and I can call functions correctly inside the library but I need to
invoke one function which has this function definition:
>
char ** CAPAPI McSearch(HMCLIN K Handle,
short nSearchType,
short nNoSelect,
char **pSelect,
short nNoWhere,
char **pWhere,
char **pData,
int iTimeout);
>
For **pSelect I want to pass in an array of char points, which in C
would be declared as
>
char *pData[] = { "ADDR", "POSTCODE" };
>
Can someone tell me how use pointers + char pointers together in
python with ctypes please?

# create an array that holds two pointers to 'char *', and fill it with data:
pData = (c_char_p * 2)()
pData[0] = "ADDR"
pData[1] = "POSTCODE"

# Another way:
pData = (c_char_p * 2)("ADDR", "POSTCODE")

Thomas

[Philluminati]

Re: Working with ctypes and char** data type

On Jul 24, 4:03 pm, Thomas Heller <thel...@python .netwrote:

Philluminati schrieb:
>
>
>

I'm a bit of a python newbie and I need to wrap a C library.

>

I can initialise the library using CDLL('mcclient. so')

>

and I can call functions correctly inside the library but I need to
invoke one function which has this function definition:

>

char ** CAPAPI McSearch(HMCLIN K Handle,
                        short nSearchType,
                        short nNoSelect,
                        char **pSelect,
                        short nNoWhere,
                        char **pWhere,
                        char **pData,
                        int iTimeout);

>

For **pSelect I want to pass in an array of char points, which in C
would be declared as

>

char *pData[] = { "ADDR", "POSTCODE" };

>

Can someone tell me how use pointers + char pointers together in
python with ctypes please?

>
# create an array that holds two pointers to 'char *', and fill it with data:
pData = (c_char_p * 2)()
pData[0] = "ADDR"
pData[1] = "POSTCODE"
>
# Another way:
pData = (c_char_p * 2)("ADDR", "POSTCODE")
>
Thomas

Thank you Thomas for your reply. I also got it working in a slightly
less sophisticated manor like this:

SelectType = c_char_p * 2
select = SelectType("ADD R", "POSTCODE")
ptr = pointer(select)

Anyway, thanks for taking the time to reply!

Phill