User manual

mikroPascal PRO for dsPIC30/33 and PIC24
MikroElektronika
210
Note: Comparing pointers pointing to different objects/arrays can be performed at programmer’s own responsibility — a
precise overview of data’s physical storage is required.
Pointer Addition
You can use Inc to add an integral value to a pointer. The result of addition is dened only if the pointer points to an
element of an array and if the result is a pointer pointing to the same array (or one element beyond it).
If a pointer is declared to point to type, adding an integral value n to the pointer increments the pointer value by n *
sizeof(type) as long as the pointer remains within the legal range (rst element to one beyond the last element). If
type has a size of 10 bytes, then adding 5 to a pointer to type advances the pointer 50 bytes in memory.
For example:
var
a : array[10] of byte; // array a containing 10 elements of type byte
ptr : ^byte; // pointer to byte
begin
ptr := @a[0]; // ptr is pointer to byte, pointing to a[0]
ptr := ptr + 3; // ptr+3 is a pointer pointing to a[3]
ptr^ := 6; // a[3] now equals 6
Inc(ptr); // ptr now points to the next element of array a: a[4]
end.
Also, you may sum values pointed to by pointers.
For example:
var
i, j, x : byte; // variables
ptr1 : ^byte; // pointers to byte
ptr2 : ^byte;
begin
i := 10; // assign value 10 to variable; i is at the address 0x0038
j := 5; // assign value 10 to variable; j is at the address 0x003A
ptr1 := @i; // ptr1 is pointer to byte, pointing to i
ptr2 := @j; // ptr2 is a pointer pointing to j
x := ptr1^ + ptr2^; // result is equal to the sum of the values pointed to; x = 5
end.
Pointer Subtraction
Similar to addition, you can use Dec to subtract an integral value from a pointer.
If a pointer is declared to point to type, subtracting an integral value n from the the pointer decrements the pointer
value by n * sizeof(type) as long as the pointer remains within the legal range (rst element to one beyond the
last element). If type has a size of 10 bytes, then subtracting 5 from a pointer to type pushes back the pointer 50 bytes
in memory.