Member Avatar for el33t

Hi,

Is this a valid while loop? :

while((grid[tr][tc]=='0'||grid[tr][tc]==s[i]) && tr<row && count<strlen(s))
       { ++count;
         ++tr;
       }

Although the full program compiles fine, but sometimes my program crashes during runtime giving me a "Access violation(Segmentation Fault)" error and the debugger points to this loop statement... By the way, I'm using dev c++ ...

Regards,

Edited by el33t
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  • Latest Post Latest Post by Gribouillis

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Nice fix by — the runtime crash was almost certainly caused by evaluating grid[tr][tc] before verifying tr is inside the array. In C/C++ the && operator short‑circuits left‑to‑right, so putting the bounds check first prevents an out‑of‑bounds access. That ordering change explains why the crash went away for .

Extra safe practices to avoid similar problems:

  • Precompute the string length once instead of calling strlen repeatedly; strlen returns an unsigned size_t, so use size_t for counters to avoid signed/unsigned issues.
  • Check every index you use (row and column bounds, and any index into s) and verify pointers (e.g., grid[tr] is not NULL) before dereferencing.
  • Watch for accidental use of the bitwise & or | instead of &&/|| — those do not short‑circuit and will evaluate both sides.
  • Add defensive assertions or explicit checks before the loop so the loop condition is not the only place that enforces invariants.

Example pattern (adapt to your types and column bounds):

size_t len = strlen(s);
size_t cnt = 0;

/* ensure tc < cols and grid rows are valid before loop */
while (tr < row && cnt < len && grid[tr] != NULL && tc < cols &&
       (grid[tr][tc] == '0' || grid[tr][tc] == s[i])) {
    ++cnt;
    ++tr;
}

Debugging tips: enable compiler warnings (-Wall -Wextra), run with AddressSanitizer (-fsanitize=address) or valgrind to catch invalid memory access, and use assertions or a debugger to inspect tr, tc, i, and pointer values at the crash site. These steps make it much easier to find the exact out‑of‑range access if it recurs.

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Member Avatar for Gribouillis

I suggest to write it as

while((tr < row) && (grid[tr][tc]=='0'||grid[tr][tc]==s[i]) && (count<strlen(s)))
       { ++count;
         ++tr;
       }

If tr < row fails, grid[tr] will not be computed :)

Member Avatar for el33t

WOW!! You suggestion worked!! My program no more crashes during runtime ! THANKS!

Member Avatar for Gribouillis

hehe !

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