SAS/C C++ Development System User's Guide, Release 6.50

Pointer Qualification Conversions

Compilers for ANSI C and older C++ compilers allow implicit pointer qualification conversions such as int** to const int** that are not type-safe. For example:

void set_it( const int** target, const int* source ) { *target = source; } void test_it( const int* const_ptr ) { int* nonconst_ptr; // Get a non-const copy of const_ptr // without casts!! // The first argument uses the old unsafe // implicit conversion. set_it( &nonconst_ptr, const_ptr ); *nonconst_ptr = 0; // assignment through // const pointer }

To avoid a similar problem with the C++ type system, the draft version of C++ allows only a subset of the implicit qualification conversions allowed in ANSI C. This subset can be summarized as follows:

Conversion of single level pointers work as they did in ANSI C.
With multiple pointer levels, when qualifiers change on a pointed to type, intermediate pointed to types in the target type must be const . For example, an int** pointer cannot be implicitly converted to const int** but it can be implicitly converted to
const int* const *
.

For more information on implicit pointer qualification conversions, refer to section 4.4 of the ISO C++ draft.

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