bug428.cpp

1    #include <stdio.h>
2    #define LENGTH 10
3    char a[LENGTH] = "567891234";
4    int ith_character( int );
5
6    int main()
7        {
8        int len = sizeof(a[LENGTH]);
9        printf(
10           "It's time to celebrate"
11           " the %cth of July\n",
12           ith_character( len-2 ) );
13       return 0;
14       }
15
16   int ith_character( int n )
17       {
18       return a[n];
19       }

In preparing a celebratory banner to honor his nation's birth the programmer noticed that a key character was missing from the expected output string. What went wrong?

bug428.cpp lint Output

--- Module:   bug428.cpp

During Specific Walk:
  File bug428.cpp line 12: ith_character(-1)
bug428.cpp(18) : Warning 428: negative subscript (-1) in operator '['
    [Reference: file bug428.cpp: lines 8, 12, 18]

Reference Manual Explanation

428    negative subscript (Integer) in operator 'String'  -- A negative
       integer was added to an array or to a pointer to an allocated
       area (allocated by malloc, operator new, etc.) This message is
       not given for pointers whose origin is unknown since a negative
       subscript is, in general, legal.

       The addition could have occurred as part of a subscript operation
       or as part of a pointer arithmetic operation.  The operator is
       denoted by String.  The value of the integer is given by Integer.