Tandy 1000 Basic Reference Manual page 337

Chapter 10 I BASIC Keywords
VARPTR Function
VARPTR (variable)
VARPTR ([#]buffer)
Returns the offset into BASIC's data segment of a variable or a
disk buffer.
Variable
is a numeric or string variable.
Buffer is the number assigned to the file when you opened it.
The number sign is optional. It is provided for compatibility with
other BASICs.
VARPTR can help you locate a value in memory. When used
with
Variable,
it returns the address of the first byte of data
identified with
variable.
See the section "How Variables
are
Stored" in Chapter 11 for the format.
If the
variable
you specify has not been assigned a value, an "Il-
legal function call" occurs.
When used with sequential access files, VARPTR returns the
starting address of the disk buffer. When used with direct access
files, VARPTR returns the address of the FIELD buffer.
If you specify a
buffer
that was not allocated when loading
BASIC, a "Bad file number" error occurs. (See Chapter 2 for in-
formation on how to load BASIC.)
The offset returned is an integer in the range -32768 to 32767.
It is always an offset into BASIC's data segment, regardless of
whether you have executed
a
DEF SEG to change the segment.
VARPTR is used primarily to pass a value to a n assembly
language subroutine via USR. Since VARPTR returns an offset
that indicates where the value of a variable is stored,
you can
pass this address to an assembly-language subroutine as the ar-
gument of USR. The subroutine can then extract the contents of
the variable with the help of the address that you have supplied
to it.
If VARPTR returns a negative address, add it to 65536 to obtain
the actual address.
335