segmentation fault while using ctypes
MRAB
google at mrabarnett.plus.com
Tue Apr 14 19:00:03 EDT 2009
sanket wrote:
> 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");
>
You should check the value of 'fp' here.
> data = (signed short *)malloc(sizeof(signed short) * N_BLOCKS);
>
You should check the value of 'data' here.
> whereami = WAVE_HEADER_SIZE;
What is 'whereami'?
> while((!feof(fp)) && (fp_more == 1) && !ferror(fp)){
> fp_data_size = fread(data,sizeof(signed short),N_BLOCKS,fp);
'fp_data_size' will be the number of signed shorts read, not the number
of bytes. Is this OK?
> whereami += fp_data_size;
The final value of 'whereami' will be WAVE_HEADER_SIZE + the total
number of signed shorts read.
> fp_more = fp_feed_short(fooid,data,fp_data_size); // call to some
> library funtion
> } //end while
>
> /* some arithmetic calculations here */
>
> n = my_fp_calculate(fooid,audio_length,fp_fingerprint,&fit,&dom);
>
> if (data != NULL)
> free(data)
I don't that 'free()' will complain if 'data' happens to be NULL,
although you should've already checked whether 'data' is NULL when you
malloc'ed! :-)
> 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
> --
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>
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