Thread: In GDB no segmentation fault but while running segmentation fault

  1. #1
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    In GDB no segmentation fault but while running segmentation fault

    I am having segmentation fault while running this code Ideone.com - yU80Bd - Online C++0x Compiler & Debugging Tool .. The problem is when I run it in GDB, the code runs fine and excellent. Why is this gdb no segfault but running every other place is segmentation fault?
    here is the problem I am trying to solve Chef and Codes | CodeChef

  2. #2
    Hurry Slowly vart's Avatar
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    when you access txtF[pos] you never check that pos is not out-of-bounds

    also you should not use magic numbers 97 and 122
    All problems in computer science can be solved by another level of indirection,
    except for the problem of too many layers of indirection.
    David J. Wheeler

  3. #3
    - - - - - - - - oogabooga's Avatar
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    It's crashing because you don't check for non-alphabetic characters in the loop that counts the frequencies. Something like this will fix it:
    Code:
            for(int i = 0; i < cipherText.size(); ++i) {
                char c = tolower(cipherText[i]);
                if (c < 'a' || c > 'z')
                    continue;
                ++cipherF[c - 'a'].frequency;
            }
    Without that check, the exclamation point at the end of "dummy!" will cause the incrementation of cipherF[-64]. This apparently overwrites something critical and the program crashes when main returns.

    When the program runs under gdb, it has a somewhat different layout and the crash doesn't happen.
    The cost of software maintenance increases with the square of the programmer's creativity. - Robert D. Bliss

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