Pointer types

• POINTER: Is a general pointer type. Variables of this type may be used as temporal storage for pointer values, i.e., values of addresses of program elements (variables, functions or procedures) in the space of memory locations at run time.

  Example: VAR Ppa: POINTER;

• Typed pointers: They are specific pointer types. Variables of specific pointer type may hold values of addresses of program elements of the specified type in the space of memory locations at run time.

  The syntax of the declaration is:
  <pointer type identifier> = ^<type identifier>
  It defines a new pointer type to element values of the identifier type, which may be a simple or structured type.

  Example:

           Ptra = ^Train;
           Train = Record
                  Engine: STRING[6];
                  Wagon: ARRAY[1 .. 16] of REAL;
                  Follows: Ptra;
                 END;

  If PTrain: Ptra is declared in the VAR subsection of DECL, then the pointer variable PTrain is supposed to point to a record with the shown structure. The variable PTrain^.Wagon[3] refers to the third array element of the field Wagon of the Train type record pointed by PTrain.

  These user's declared records are seldom used in GLIDER because messages suffices for almost all the uses and they are internally handled by GLIDER instructions and procedures.

Pointer variable value assignment results from dynamic memory allocation (Pascal procedure NEW) or from direct assignment of memory addresses values, as returned by function ADDR( ), for instance. Pointer variables must be carefully used.