Python 3.4.3 ctypes: Trying to pass a structure to a function as an output parameter fails -

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here's given vendor describe function.

typedef struct {    float    distance_sm;    float    distance_nm;    short    fuel_stops;    char     flight_time[8];    char     block_time[8];    char     departure_time[8];    char     departure_date[12];    char     arrival_time[8];    char     arrival_date[12];    char     timezone_change[8];    char     messages[fosapi_msg_len]; } fos_leg;  fos_extern_c bool dll_exp_util fos_calc_flight(    char *leg_date,               // in: leg date                          (    char *leg_time,              // in: leg time                          (    char *airport_from,          // in: airport icao(4) or iata(3)   (kokc)    char *airport_to,            // in: airport icao(4) or iata(3)    char *aircraft_type,         // in: character aircraft type (max len = 4)    fos_leg  *fos_leg,            // in: allocated space fos_leg    char errors[fosapi_msg_len],         // in: 256 bytes  out: error messages    bool arrival_date_time=false,    // in: true = leg_date , leg_time arrival, calculate departure    char *airport_from_prefix=null,  // in: airport icao code(2)    char *airport_to_prefix=null);   // in: airport icao code(2)

so here's code i'm trying access function with. seems problem way i'm trying pass structure output parameter function. 

import ctypes  mydll = ctypes.windll.loadlibrary("c:\\fos\\fosutil.dll")  class fos_leg(ctypes.structure):     _fields_ = [     ("distance_sm",     ctypes.c_float),     ("distance_nm",     ctypes.c_float),     ("fuel_stops",      ctypes.c_short),     ("flight_time",     ctypes.c_char),     ("block_time",      ctypes.c_char),     ("departure_time",  ctypes.c_char),     ("departure_date",  ctypes.c_char),     ("arrival_time",    ctypes.c_char),     ("arrival_date",    ctypes.c_char),     ("timezone_change", ctypes.c_char),     ("messages",        ctypes.c_char)]  fos_leg   = ctypes.pointer(fos_leg) error_out = ctypes.c_char  mydll._fos_calc_flight("04042014","0800","kokc","katl","h25b",fos_leg,error_out,1,"ap","ap")

here's error returned.

traceback (most recent call last): file "test.py", line 28, in mydll._fos_calc_flight("04042014","0800","kokc","katl","h25b",fos_leg,er ror_out,1,"ap","ap") ctypes.argumenterror: argument 6: : don't know how convert parameter 6

thanks assistance

untested, structure should more like:

class fos_leg(ctypes.structure):     _fields_ = [     ("distance_sm",     ctypes.c_float),     ("distance_nm",     ctypes.c_float),     ("fuel_stops",      ctypes.c_short),     ("flight_time",     ctypes.c_char * 8),     ("block_time",      ctypes.c_char * 8),     ("departure_time",  ctypes.c_char * 8),     ("departure_date",  ctypes.c_char * 12),     ("arrival_time",    ctypes.c_char * 8),     ("arrival_date",    ctypes.c_char * 12),     ("timezone_change", ctypes.c_char * 8),     ("messages",        ctypes.c_char * fosapi_msg_len)]

next should declare arguments , return type of function:

mydll._fos_calc_flight.argtypes = [ctypes.c_char_p,ctypes.c_char_p,ctypes.c_char_p,ctypes.c_char_p,ctypes.c_char_p,ctypes.pointer(fos_leg),ctypes.c_char_p,ctypes.c_bool,ctypes.c_char_p,ctypes.c_char_p] mydll._fos_calc_flight.restype = ctypes.c_bool

finally, output parameters need instances of types required. pointer declares type, want create instance of structure:

fos_leg = fos_leg()

error_out needs writable string:

error_out = ctypes.create_string_buffer(fosapi_msg_len)

then call function reference structure:

mydll._fos_calc_flight(b"04042014",b"0800",b"kokc",b"katl",b"h25b",ctypes.byref(fos_leg),error_out,1,b"ap",b"ap")

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