bug1561.cpp

1    #include <stdio.h>
2
3    const char *buf = "showers";
4
5    void h( const char *&q )
6        { q = buf; }
7   
8    int main()
9        {
10       char *p;
11
12       h( p );
13       printf( "%s\n", buf );
14       p[0] = 'f';   p[1] = 'l';
15       printf( "%s\n", buf );
16       return 0;
17       }

This program converts "showers" into "flowers" which might be nice but since "showers" was initially const how was const integrity shattered?

bug1561.cpp lint Output

--- Module:   bug1561.cpp
         _
    h( p );
bug1561.cpp(12) : Warning 1561: Reference initialization causes loss of
    const/volatile integrity (arg. no. 1)

Reference Manual Explanation

       
1561  Reference initialization causes loss of const/volatile integrity (Context)  -- 
      A reference initialization is resulting in a capability gain that can cause a 
      loss of const or volatile integrity.

      Typically the message is given on initializing a non-const reference with a 
      const.  For example:

                void f( int &x );
                const int n = 0;
                ...

                f(n);

      Here, function f() could assign a value to its argument and thereby modify n, 
      which is declared to be const.

      The message can also be issued when a pointer is initialized.  Consider the 
      following example.

                void h( const int *&q );
                int *p;
                ...

                h(p);

      It might seem that passing a regular (i.e., non-const) pointer to a const int * 
      could cause no harm.  That would be correct if it were not for the reference.  
      If function h() were to assign a pointer to const to its parameter q then upon 
      return from the call, p could be used to modify const data.

      There are many subtle cases that can boggle the mind.  See the commentary to Message 605.