Const Quick-Ref.cpp

//Const Quick-Ref
 
        int               variable_integer = 39;
  const int               constant_integer = 42;
  const int *         var_ptr_to_const_int = &constant_integer;
  int const *    also_var_ptr_to_const_int = &constant_integer;
        int * const const_ptr_to_var_int   = &variable_integer;
  int const * const const_ptr_to_const_int = &constant_integer;
        int &                   ref_to_int = variable_integer;
  const int &             ref_to_const_int = constant_integer;
  int const &        also_ref_to_const_int = constant_integer;
// error: ‘const’ qualifiers cannot be applied to ‘int&’
//      int & const const_ref_to_var_int   = variable_integer; 
// error: ‘const’ qualifiers cannot be applied to ‘const int&’
//int const & const const_ref_to_const_int = constant_integer; 
 
        int                            return_int() { return variable_integer; }
  const int                      return_const_int() { return constant_integer; }
  const int *             return_ptr_to_const_int() { return var_ptr_to_const_int; }
  int const *        also_return_ptr_to_const_int() { return also_var_ptr_to_const_int; }
        int * const return_const_ptr_to_var_int()   { return const_ptr_to_var_int; }
  int const * const return_const_ptr_to_const_int() { return const_ptr_to_const_int; }
  const int &             return_ref_to_const_int() { return constant_integer; }
  int const &        also_return_ref_to_const_int() { return constant_integer; }

struct big_t {
  big_t(int value) : stuff(value) { }
  void setter_method(int newval) { stuff = newval; }
  int getter_method() const { return stuff; }
  int stuff;
};
 
int  func_copy(                int         read_by_cpy) { return read_by_cpy; }
void func_edit_by_ref(         int       & edit_by_ref) { edit_by_ref = 42; }
void func_edit_by_ref_mem(   big_t       & edit_by_ref) { edit_by_ref.stuff = 42; }
int  func_read_const_ref(      int const & read_by_ref) { return read_by_ref; }
int  func_read_const_ref_mem(big_t const & read_by_ref) { return read_by_ref.stuff; }
void func_edit_by_ptr(         int       * edit_by_ptr) { *edit_by_ptr = 42; }
void func_edit_by_ptr_mem(   big_t       * edit_by_ptr) { edit_by_ptr->stuff = 42; }
int  func_read_const_ptr(      int const * read_by_ptr) { return *read_by_ptr; }
int  func_read_const_ptr_mem(big_t const * read_by_ptr) { return read_by_ptr->stuff; }

const big_t constant_big(constant_integer);
      big_t variable_big(variable_integer);

int main(void) {
    variable_integer = 56;
 // error: assignment of read-only variable ‘constant_integer’
 // constant_integer = 77;
 // error: invalid lvalue in unary ‘&’
 // var_ptr_to_const_int = &33;
    var_ptr_to_const_int = &variable_integer;
    also_var_ptr_to_const_int = &variable_integer;
    *const_ptr_to_var_int = 22;
 // error: assignment of read-only location
 // *const_ptr_to_const_int = 26;
    func_copy(variable_integer);
    func_copy(constant_integer);
    func_edit_by_ref(variable_integer);
 // error: invalid initialization of reference of type ‘int&’ from expression of type ‘const int’
 // func_edit_by_ref(constant_integer);
 // error: invalid initialization of reference of type ‘int&’ from expression of type ‘const int’
 // func_edit_by_ref(ref_to_const_int);
 // error: invalid initialization of reference of type ‘int&’ from expression of type ‘const int’
 // func_edit_by_ref(*var_ptr_to_const_int);
    func_edit_by_ref(*const_ptr_to_var_int);
 // error: invalid initialization of reference of type ‘int&’ from expression of type ‘const int’
 // func_edit_by_ref(*const_ptr_to_const_int);
    func_edit_by_ref_mem(variable_big);
 // error: invalid initialization of reference of type ‘big_t&’ from expression of type ‘const big_t’
 // func_edit_by_ref_mem(constant_big);
    func_read_const_ref_mem(variable_big);
    func_read_const_ref_mem(constant_big);
    func_read_const_ptr(&variable_integer);
    func_read_const_ptr(&constant_integer);
    func_edit_by_ptr(&variable_integer);
 // error: invalid conversion from ‘const int*’ to ‘int*’
 // func_edit_by_ptr(&constant_integer);
 // error: invalid conversion from ‘const int*’ to ‘int*’
 // func_edit_by_ptr(var_ptr_to_const_int);
    func_edit_by_ptr(const_ptr_to_var_int);
    func_edit_by_ptr(const_ptr_to_var_int);
 // invalid conversion from ‘const int* const’ to ‘int*’
 // func_edit_by_ptr(const_ptr_to_const_int);
    func_edit_by_ptr_mem(&variable_big);
 // error: invalid conversion from ‘const big_t*’ to ‘big_t*’
 // func_edit_by_ptr_mem(&constant_big);
    variable_big.setter_method(11);
 // error: passing ‘const big_t’ as ‘this’ argument of ‘void big_t::setter_method(int)’ discards qualifiers
 // constant_big.setter_method(12);
    return 0;
}