GW BASIC String Descriptor address using VARPTR

When using the VARPTR function in GWBASIC it returns the address of the variable or array. Except for Strings, it returns the address of a 3 byte string descriptor. To get the address of the string we need to do some work

N$="Nick"

SA=VARPTR(N$)

PRINT PEEK(SA) 'the length of the string

PRINT PEEK(SA+1) 'lower 8 bits of address

PRINT PEEK(SA+2) 'higher 8 bits of address

to compute string address we perform the following calculation

smem#=peek(SA+2)*256+peek(SA+1) 'should point to string memory - this does what SADD function does in QBASIC/QuickBASIC

if you use integer variable % you will get an overflow. you can still convert to an integer with the following code

mem$=chr$(peek(SA+1))+chr$(peek(SA+2)) ' this converts our peek info to a 2 character string

smem%=CVI(mem$) ' we can convert the 2 character string to an integer using the CVI function without causing a buffer overflow

oh wait there is even more

now that we have the address of the string we can

print the first letter of our string by

print chr$(peek(smem%)) 'increase the smem% variable to access the other letter like smem%+1 for second letter and so on

and we can even change the string contents with poke

poke smem%,ASC("K") 'this changes N$ from Nick to Kick