Thread: string changing problem

Hello everyone.
Im playing with one parser that is not working.
It's failing with segment.error, and I could not fix it, since im not good at all in c .
I think the issue is in one place, where im trying to change one string to other one. It's always failing on third step - ending with that segm.error.
Im calling fillcd, where cid2cid "function" is used to modify the buf string.
After third succesfully changed string it fails…Isnt there a memory problem?

buf: 3000/000/00/MOY,3000/000/00/MAX,3000/000/00/CUM,3000/000/00/ECH,3004/000/00/CUM,3004/000/00/ECH,3004/000/00/MOY,3004/000/00/MAX,3004/001/00/CUM,3004/001/00/ECH,3004/001/00/MOY,3004/001/00/MAX,3008/000/00/CUM,3008/000/00/ECH,3008/000/00/MOY

Output in cd variable should be like: MOY_3000_000_00,MAX_3000_000_00,CUM_3000_000_00, ….

Thanks for any ideas !

Script:

Code:

...
char *cid2cid(char *s){
  static char tmp[20];
      
  strcpy(tmp, s);
  s[0]=tmp[12]; 
  s[1]=tmp[13];
  s[2]=tmp[14];
  s[3]='_';
  s[4]=tmp[0];
  s[5]=tmp[1];
  s[6]=tmp[2];
  s[7]=tmp[3];
  s[8]='_';
  s[9]=tmp[5];
  s[10]=tmp[6];
  s[11]=tmp[7];
  s[12]='_';
  s[13]=tmp[9];
  s[14]=tmp[10];
  s[15]='\0';
  return s;
}

int fillcd( char *buf, char *cd[], FILE *f ) {
  char *p;
  int i;  
  cd[0]=cid2cid(strdup(strtok(buf,",")));
  i=1;
  while ( (p=strtok(NULL, ",")) != NULL ) cd[i++]=strdup(cid2cid(p));
  cd[i]=strdup("FINITO");
  return i;
}

…

char buf[1000], classn[100], *procstr[100], *cd[200];
counters=fillcd(inbuf,cd, fout);

Thanks for any ideas !

The string you're making longer is the result of a call to strdup().
Which will (as far as you can assume) will only store as many characters as originally stored.

Perhaps
1. Validate your data before assuming that the format is correct.
2. Add a condition to your while loop which limits the range of i to be that of the array.

> int fillcd( char *buf, char *cd[], FILE *f )
You don't use f in this function.

Originally Posted by dusoo

The strange thing about my error is, that few days ago it was running without problem with the same data. Now it is failing (no data change). On other system the same parser is working without problem...So i dont have a clue what's going on. Could be there a memory allocation problem? thanks

Did you understand the post by root4?

There is a difference between:
char *str = "something";
and
char str[] = "something";

In the latter case, you can write to the original string because the string memory is actually inside str as an array, in the first one, you can't, because the string itself is stored in "read-only" memory. This DOES vary between compilers - but shouldn't make any difference which machine you run it on.

Edit: Note that this line:

Code:

 while ( (p=strtok(NULL, ",")) != NULL ) cd[i++]=strdup(cid2cid(p));

first writes to p, the copies the resulting string.

One solution to avoid all of that would be:

Code:

char *cid2cid(char *s){
  static char tmp[20];
      
  tmp[0]=s[12]; 
  tmp[1]=s[13];
  tmp[2]=s[14];
  tmp[3]='_';
  tmp[4]=s[0];
  tmp[5]=s[1];
  tmp[6]=s[2];
  tmp[7]=s[3];
  tmp[8]='_';
  tmp[9]=s[5];
  tmp[10]=s[6];
  tmp[11]=s[7];
  tmp[12]='_';
  tmp[13]=s[9];
  tmp[14]=s[10];
  tmp[15]='\0';
  return tmp;
}

It's ok to return tmp since tmp is static, so it doesn't go away when the function returns.
[And the above code is a tiny bit faster, since it doesn't copy s into tmp first.]

--
Mats