What is an address operator and pointer dereferencing?A very powerful facility within the C programming language is the ability to manipulate the memory pointers as though they are data (just like any other number). XCSB also supports memory pointers similar to those of C. A very useful ability within C is the ability to quickly and easily determin the address of a variable and assign it to a pointer so that the variable can subsequently be manipulated indirectly.
The XCSB address of operator is the & (ampersand character).
The XCSB pointer dereference operator is the * (asterisk character).
X = &Y means assign the address of Y to the variable X W = *X means assign the value at the location pointed to by X to the variable W (in this case X points to Y, so indirectly access the contents of Y and assign it to W)
simple example showing the use of pointers and addresses
Non-pointer versionif a < b then if x < y then if a < x then a = a + 1 else x = x + 1 endif else if a < y then a = a + 1 else y = y + 1 endif endif else if x < y then if b < x then b = b + 1 else x = x + 1 endif else if b < y then b = b + 1 else y = y + 1 endif endif endif Pointer versionif a < b then s1 = &a else s1 = &b endif if x < y then s2 = &x else s2 = &y endif if *s1 >= *s2 then s1 = s2 endif *s1 = *s1 + 1
Why does XCSB not need PEEK and POKE functions?
Since XCSB has pointer capabilities it is not necessary to have the PEEK and POKE functions necessary in other versions of BASIC. By simply using the address directly as a pointer, XCSB achives the functionality of both PEEK and POKE and whereas use of PEEK and POKE would interfere with optimisation, using pointers does not have this drawback.
simple example showing the use of pointers in place of PEEK and POKE
Using PEEK and POKEPOKE(123, PEEK(123)+1) Using pointers*123 = (*123) + 1