bug671.cpp

1     #include <string.h>
2
3     void process( int *, int * );
4     #define N 100
5
6     void f( int n )
7         {
8         int *p, *q;
9         int i;
10
11        p = new int[ N*2 ];
12        q = new int[ N ];
13        if( !p  || !q ) return;
14        if( n >= 0 ) memset( p, 1, N*2 );
15        else for( i = 0; i < N*2; i++ )
16            p[i] = i;
17        memset( q, 0, n );
18        process( p, q );
19        }

Calling this function has caused strange and erratic behavior. Can you spot the problem?

bug671.cpp lint Output

--- Module:   bug671.cpp
                    _
    memset( q, 0, n );
bug671.cpp(17) : Info 732: Loss of sign (arg. no. 3) (int to unsigned int)
bug671.cpp(17) : Warning 671: Possibly passing to function memset(void *,
    int, unsigned int) a negative value (-1), arg. no. 3
    _
    }
bug671.cpp(19) : Warning 429: Custodial pointer 'p' (line 8) has not
    been freed or returned
bug671.cpp(19) : Warning 429: Custodial pointer 'q' (line 8) has not
    been freed or returned

Reference Manual Explanation

671    Possibly passing to function Symbol a negative value (Integer),
       Context  -- An integral value that may possibly be negative is
       being passed to a function that is expecting only positive values
       for a particular argument.  The message contains the name of the
       function (Symbol), the questionable value (Integer) and the
       argument number (Context).  The function may be a standard
       library function designed to accept only positive values such as
       malloc or memcpy (third argument), or may have been identified by
       the user as such through the -function or -sem options.
       See message 422 for an example and further explanation.