confused about strlen()

perfect_circle · 02-25-2005, 09:41 PM

Quote:

also, when i convert the string to integers, it converts it into the integer value of the ascii code, not the equivalent integer. so '0' becomes 48, '1' becomes 49, etc etc. so right now i subtract 48, and '0' = 0, '1'=1, and so on, but this seems like a bit of an ugly hack to me. is there another preferred way of doing this?

Actualy more or less thats what atoi does:
when you have a string "123" or better '1' '2' '3' '\0' what atoi will do is ((('1'-48)*10 + ('2'-48))*10+'3'-48)*10=100 +20 +3=123 using a for loop

Dark_Helmet · 02-26-2005, 03:12 PM

I know I'm coming into this discussion late, but here's a slightly modified version of your code mcd.

Code:

char *getstring ( void )
{
  char *q;  /* There is no need to pass in q if you disregard its value :) */
  int size_allocated = 5*sizeof( char );   /* initially allocate this amount */

  q = malloc( size_allocated );
  if (q==0)                                /* I got this from RUTE Users Tutorial =) */
  {
    perror("malloc failed!\n);
    abort();
  }
  memset( q, 0, size_allocated );

  printf("Please input a number\n");

  int c=0;
  while (q[c-1] != '\n')                   /* if the users types a \n, the next time this is processed it will exit */
  {
    if (c == ( size_allocated - 2 ))       /* size_allocated is the size of your buffer.
                                              reallocate when the next character would overwrite the final NULL */
    {
      q = realloc(q, size_allocated * 2);
      if (q==0)
      {
        perror("realloc failed!\n);
        abort();
      }
      memset( q + size_allocated, 0, size_allocated );
      size_allocated = size_allocated*2;
    }
    q[c]=getchar();                        /* after all that, this is what's being done, lol */
    c++;
  }

  return q;
}

That's how I would approach it if I were to follow what you're shooting for. Obviously, the stuff in blue is modified/new code. I use memset() to guarantee your string has (at least one) final NULL character. The memset after reallocation should leave the previous string unaltered, but initialize the new portion.

While this method will allow dynamic changing of the buffer size, it's a little difficult to handle mistakes. Say the user types in a letter by accident, or hits the backspace/delete key.

EDIT:
I accidentally had the condition listed incorrectly. It was "c < ( size_allocated - 2 )", and it should be what I have written now: "c == ( size_allocated - 2 )"

perfect_circle · 02-26-2005, 04:01 PM

Quote:

int c=0;
while (q[c-1] != '\n') /* if the users types a \n, the next time this is processed it will exit */

I don't like this one.
q[-1] is out of the range of the string

Dark_Helmet · 02-26-2005, 04:56 PM

That's a good point. A do-while loop would probably be better:

Code:

int c=0;
do
{

   ...

  c++;
} while ( q[c-1] != '\n' );

mcd · 02-26-2005, 08:04 PM

great, thanks for the comments guys! i'm making the changes now.