Pointers and references: Difference between revisions

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=={{header|ALGOL 68}}==

The following code creates a pointer to an INT variable

The following code creates a pointer to an INT variable:

INT var := 3;

REF INT pointer := var;

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INT v = pointer; # sets v to the value of var (i.e. 3) #

REF INT(pointer) := 42; # sets var to 42 #

Change the pointer to refer to another object

Change the pointer to refer to another object:

INT othervar;

pointer := othervar;

Change the pointer to not point to any object

Change the pointer to not point to any object:

pointer := NIL; # 0 cannot be cast to NIL #

Get a pointer to the first element of an array:

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The following code create a constant reference to an INT variable:

REF INT alias = var;

Access the integer variable through the reference

Access the integer variable through the reference:

INT v2 = alias; # sets v2 to the value of var, that is, 3 #

alias := 42; # sets var to 42 #

References cannot be changed to refer to other objects, and cannot (legally) made to refer to no object.

~~pointers~~ can be compared, but only for equality

Pointers can be compared, but only for equality:

printf(($"alias "b("IS","ISNT")" var!"l$, alias IS var));

Output: alias IS var!

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Changing the reference to refer to another object of the array is not possible.

ALGOL 68 also allows pointers to slices of rows and/or columns of arrays

ALGOL 68 also allows pointers to slices of rows and/or columns of arrays:

[9,9]INT sudoku;

REF [,]INT middle;

middle := sudoku[3:5,3:5];

# This includes pointers to slices character arrays #

This includes pointers to slices character arrays:

[30]CHAR hay stack := "straw straw needle straw straw";

REF[]CHAR needle = hay stack[13:18];