segmentation fault while using ctypes

[patelss23]

Hello All,

I am dealing with this weird bug.
I have a function in C and I have written python bindings for it using
ctypes.

I can call this function for couple of times and then suddenly it
gives me seg fault.
But I can call same function from a C code for any number of times.

I cannot get what's going on.

here is my code.

/**********************************************/
/* C Function I am calling */

int get_hash(char *filename,int rate,int ch,unsigned char* hash,
unsigned int* hash_size,short* avg_f,short* avg_d){
 
/* some variable declarations here */
fp = fopen(filename,"rb");
 
data = (signed short *)malloc(sizeof(signed short) * N_BLOCKS);
 
whereami = WAVE_HEADER_SIZE;
while((!feof(fp)) && (fp_more == 1) && !ferror(fp)){
     data_size = fread(data,sizeof(signed short),N_BLOCKS,fp);
     whereami += data_size;
     fp_more = fp_feed_short(id,data,data_size); // call to some
library funtion
 } //end while
 
/* some arithmetic calculations here */
 
  n = hash_calculate(id,length,hash,&f,&d);
 
  if (data != NULL)
      free(data)
  fclose(fp)
  return n;
 
}
 

/*** END OF C FUNCTION ******/
--------------------------------------------------------------------
Python code
---------------------------------------------------------------------

from ctypes import *
lib = cdll.LoadLibrary("/usr/lib/libclient.so")
 
def my_func(filename,rate,ch):
    hash = (c_ubyte * 424)()
    hash_size = c_uint()
    avg_f = c_short(0)
    avg_d = c_short(0)
    n = lib.get_hash(filename,rate,ch,hash,byref(hash_size),byref
(avg_f),byref(avg_d))
    hash = None
 
def main():
    for filename in os.listdir(MY_DIR):
            print filename
            my_func(filename,100,10)
            print
"----------------------------------------------------"
 
if __name__ == "__main__":
    main()

============== END OF PYTHON CODE ==========================

Thank you in advance,
sanket

[Banfa]

You have left some important bits out of your C code particularly the declarations of all the variables in

n = hash_calculate(id,length,hash,&f,&d);

Also what do the functions fp_feed_short and hash_calculate do? Where are they declared? Where are they defined?

[patelss23]

hi Banfa,

Yeah I have declared all variables correctly in the function body, just didn't mention here. fp_feed_short is an API call to some library which returns me 1 to stop. and hash_calculate is doing some (customized) kind hasing on a file.

[Banfa]

@patelss23
Something is going wrong and you don't know what! Therefore how do you know that everything is declared and initialised correctly given you have behaviour you can't explain?