bug661.cpp

1    const int KMAX = 30;
2    double q[KMAX];
3
4    void f( double limit )
5        {
6        double s = 1;
7        int k = 0;
8        q[0] = 0;
9        while( q[k] <= limit && k < KMAX )
10           {
11           k++;
12           s = s * (k+1);
13           q[k] = q[k-1] + s;
14           }
15       }

There is a "time-bomb" lurking in this whittled-down extraction of a larger program. Can you spot it?

bug661.cpp lint Output

--- Module:   bug661.cpp
                         _
        q[k] = q[k-1] + s;
bug661.cpp  13  Warning 661: Possible access of out-of-bounds pointer
    (1 beyond end of data) by operator '['

Reference Manual Explanation

661    possible access of out-of-bounds pointer ('Integer' beyond end of
       data) by operator 'String'  -- An out-of-bounds pointer may have
       been accessed.  See message 415 for a description of the
       parameters Integer and String.  For example:
             int a[10];
             if( n <= 10 ) a[n] = 0;

       Here the programmer presumably should have written n<10.  This
       message is similar to messages 415 and 796 but differs from them
       by the degree of probability.
       See Value Tracking