C .so library Python

Question

Now my code works with a normal c library, but I need to use a .so library from Caen and I get Segmentation fault. This is the code:

from ctypes import *
lib = CDLL('./libcaenhvwrapper.so.5.56')
lib.CAENHVInitSystem.restype = c_int
lib.CAENHVInitSystem.argtypes = [c_int, c_int, c_char_p, c_char_p, c_char_p]
lib.CAENHVGetError.restype = c_int    

CAENHV_SYSTEM_TYPE_t = c_int
sy1527 = CAENHV_SYSTEM_TYPE_t(0)
sy2527 = CAENHV_SYSTEM_TYPE_t(1)
sy4527 = CAENHV_SYSTEM_TYPE_t(2)
sy5527 = CAENHV_SYSTEM_TYPE_t(3)
n568 = CAENHV_SYSTEM_TYPE_t(4)
v65xx = CAENHV_SYSTEM_TYPE_t(5)
n1470 = CAENHV_SYSTEM_TYPE_t(6)
v8100 = CAENHV_SYSTEM_TYPE_t(7)

link = c_int
LINKTYPE_TCPIP = link(0)
LINKTYPE_RS232 = link(1)
LINKTYPE_CAENET = link(2)
LINKTYPE_USB = link(3)
LINKTYPE_OPTLINK = link(4)
LINKTYPE_USB_VCP = link(5)

string15=c_char*15
address=string15('1','3','7','.','1','3','8','.','1','3','.','2','0','3','\0')

userName = c_char_p('user')
passwd = c_char_p('user')
ret_init =  lib.CAENHVInitSystem(0, 0, address, userName, passwd)

when I try to call the function I get a segmentation fault. I think the types are correctly defined. Below you can see a piece of code which works ok.

from ctypes import *
lib2 = CDLL('/lib64/libc.so.6')
string15=c_char*15
address=string15('1','3','7','.','1','3','8','.','1','3','.','2','0','3','\0')
address1=create_string_buffer('137.138.13.203')
address2=c_char_p('137.138.13.200')

userName = c_char_p('user')
passwd = c_char_p('user')

a= lib2.strncmp(address, userName, c_int(4))    
a= lib2.strncmp(userName, address, 4)
a= lib2.strncmp(address2, address, 15)

lib2.printf('%d\n', ret_init)
lib2.printf('%s\n', address)
lib2.printf('%s\n', address1)
lib2.printf('%s\n', address2)
lib2.printf('%d\n', lib2.strlen(address))
lib2.printf('%d\n', lib2.strlen(address1))
lib2.printf('%d\n', lib2.strlen(adrress2))

Looking at the available docs online, does it make a difference with you put a C string as the first argument? — chazkii, Aug 29 '14 at 10:14
You should edit your question to show the signature of `CAENHVInitSystem` as provided in the corresponding `.h` — Sylvain Leroux, Aug 29 '14 at 10:15

Sylvain Leroux · Accepted Answer · 2014-08-29T10:27:32.710

0

From a quick search:

CAENHVRESULT CAENHVInitSystem(
const char *SystemName, // In
int     LinkType,
void     *Arg,
const char *UserName,
const char *Password
);

First parameter id definitively a "pointer to char", you should declare it like that:

lib.CAENHVInitSystem.argtypes = [c_char_p, c_int, c_int, c_char_p, c_char_p, c_char_p]

In addition:

ret_init =  lib.CAENHVInitSystem(0, 0, address, userName, passwd)
#                                ^

You pass NULL as SystemName (as NULL is ((void*)0) on most systems). According to the doc I quickly read, this is not explicitly supported.

This is the first function with parameter SystemName to call, and it must be called for all the HV power supplies the user wants to control

edited Aug 29 '14 at 10:27

answered Aug 29 '14 at 10:22

Sylvain Leroux

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I tried this but it doesn't make any difference. I also tried the function CAENHV_InitSystem wchich requires an integer as first argument and the result is the same. When I try to use an invalid linktype (like a string or c_int>5) I get the right result: linktype not supported. – leonardo Aug 29 '14 at 10:27
@leonardo You have tried to pass a _valid_ string as first parameter ? – Sylvain Leroux Aug 29 '14 at 10:27
The second function still has problems, but I will try to sort it out. Thanks a lot. – leonardo Aug 29 '14 at 10:41

C .so library Python

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