ctypes

[luca72]

can you explain how to use this function :
this is the api documentation :
PREF0 short usb_tc08_get_single (
short handle,
float * temp,
short * overflow_flags,
short units);

This is the sample made in c:
int main(void)
{
short handle = 0; /* The handle to a TC-08 returned by
usb_tc08_open_unit() */
char selection = 0; /* User selection from teh main menu */
float temp[9]; /* Buffer to store temperature readings
from
the TC-08 */
int channel, reading; /* Loop counters */
int retVal = 0; /* Return value from driver calls
indication
success / error */
USBTC08_INFO unitInfo;/* Struct to hold unit information */

usb_tc08_get_single(handle, temp, NULL, USBTC08_UNITS_CENTIGRADE);
i do
strumento = ctypes.cdll.LoadLibrary('/home/luca/Desktop/luca/
progetti_eric/Pico/libusbtc08-1.7.2/src/.libs/libusbtc08.so')
strumento.usb_tc08_get_single.argtypes = [ctypes.c_short,
ctypes.c_float, ctypes.c_short, ctypes.c_short] is this correct?
strumento.usb_tc08_get_single.restype = ctypes.c_short is this
correct?
now how i can use the function?
leggo = strumento.usb_tc08_get_single(0, temp,
'NULL','USBTC08_UNITS_CENTIGRADE')
how i can define ad pas the value temp, null,USBTC08_UNITS_CENTIGRADE

thanks luca

 

[Gabriel Genellina]

can you explain how to use this function :
this is the api documentation :
PREF0 short usb_tc08_get_single (
short handle,
float * temp,
short * overflow_flags,
short units);

This is the sample made in c:
int main(void)
{
short handle = 0; /* The handle to a TC-08 returned by
usb_tc08_open_unit() */
char selection = 0; /* User selection from teh main menu */
float temp[9]; /* Buffer to store temperature readings
from
the TC-08 */
int channel, reading; /* Loop counters */
int retVal = 0; /* Return value from driver calls
indication
success / error */
USBTC08_INFO unitInfo;/* Struct to hold unit information */

usb_tc08_get_single(handle, temp, NULL, USBTC08_UNITS_CENTIGRADE);

i do
strumento = ctypes.cdll.LoadLibrary('/home/luca/Desktop/luca/
progetti_eric/Pico/libusbtc08-1.7.2/src/.libs/libusbtc08.so')
strumento.usb_tc08_get_single.argtypes = [ctypes.c_short,
ctypes.c_float, ctypes.c_short, ctypes.c_short] is this correct?

That's wrong. Second and third parameters are pointers:

# define a pointer type
c_float_p = ctypes.POINTER(ctypes.c_float)
c_short_p = ctypes.POINTER(ctypes.c_short)

usb_tc08_get_single = strumento.usb_tc08_get_single
usb_tc08_get_single.argtypes = [
ctypes.c_short,
c_float_p,
c_short_p,
ctypes.c_short]
usb_tc08_get_single.restype = ctypes.c_short

now how i can use the function?
leggo = strumento.usb_tc08_get_single(0, temp,
'NULL','USBTC08_UNITS_CENTIGRADE')

That's wrong too. In the C code, the third parameter is NULL - this
corresponds to None in Python, not the string 'NULL'.
Also, they define a temporary float array of size 9 and use it as the
second argument - we have to do the same in Python. (Note that ctypes
accepts an array in place of a pointer argument, same as C).
Last, you have to search for the value of USBTC08_UNITS_CENTIGRADE, likely
it's a #define in a .h header file. Suppose you find the corresponding
value is 42:

USBTC08_UNITS_CENTIGRADE = 42
temp = (ctypes.c_float * 9)()
handle = 0
leggo = usb_tc08_get_single(handle, temp, None, USBTC08_UNITS_CENTIGRADE)

Hope it helps,

 

[Lawrence D'Oliveiro]

c_float_p = ctypes.POINTER(ctypes.c_float)
c_short_p = ctypes.POINTER(ctypes.c_short)

I like to do

import ctypes as ct

to shorten the references:

c_float_p = ct.POINTER(ct.c_float)
c_short_p = ct.POINTER(ct.c_short)

 

[Stefan Behnel]

[3x the same thing]

You should learn to calm down and wait for an answer. Even if the problem
is urgent for you, it may not be to everyone, and spamming a newsgroup will
not help to get people in a friendly mood to write a helpful reply.

This is always worth a read:
http://www.catb.org/~esr/faqs/smart-questions.html

Stefan

 

[Aahz]

+1 QOTW

 

[CTO]

At the risk of self-promotion, you may want to try <a href="http://
.... def usb_tc08_get_single(handle: "c_short", temp: "*c_float",
overflow_flags: "*c_short", units: "c_short") -> "c_short":
.... return usb_tc08_get_single.c_function(handle, temp,
overflow_flags, units)

Make sure to properly handle your arrays, though.