> From: Lawrence Lile [mailto:llile@toastmaster.com]

...


> Here's #1 and #2 of 999 ways to NOT manipulate strings in a PIC '873:
>
> 1.  Turn on low voltage programming and forget you did this
> 2. Execute the following bug-riddled code:
>
> char array[15];
> char *pString;
>
> pString = array[0];  // [sic]  #1 should be pString = &array[0]
>
> void makestring(char c){
>     *pString++ = c;
> }
>
> printf(makestring, "Good Morning, Vietnam!");  // [sic] #2
> buffer overrun
>
> puts(array);
>

...

> I'd like to have a way to check for bounds inside the
> makestring() function,  pass it the beginning and ending
> address of the array, then generate an error or do nothing if
> pString points outside of the array in question.   I don't
> think you can have a function inside printf() that has
> arguments, though.   At least I haven't gotten anything to work yet.


Since you're already dependent on variables external to makestring(), you might
want to keep another variable indicating how many characters you've already
written.

Here's a quick and dirty sample of untested code:

#define STR_LEN 15
char array[STR_LEN];
int iString = 0;

void makestring(char c)
{
    if (iString < (STR_LEN - 1))        /* array is 0 .. STR_LEN - 1 */
    {
        array[iString] = c;
        i++;
    }
    else
    {
        /* do error stuff */
    }
}

This keeps you from referencing incorrect addresses as well as overflowing any
allocated space.

-Mike

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