Chapter 13: Memory Management
137
TI
-
89 / TI
-
92 Plus Developer Guide
Not for Distribution
Beta Version January 26, 2001
push_setfold
— Set current default folder (TI
-
BASIC version of
FolderCur
).
TokenizeSymName
— Tokenize a name and check for invalid or reserved names.
VarRecall
— Look-up a variable (returning its HSYM).
VarStore
— Store a value to a variable.
In order to use most of these routines, the variable names must be tokenized and
pushed onto the estack.
TokenizeSymName
does this as well as checking for
invalid names. There are only two routines for storing to and retrieving variable
values:
VarStore
and
VarRecall
. This is because there are many system
variables that are not in the symbol table (system variables are only accessible
through
VarStore
and
VarRecall
).
VarStore
also does extensive type checking
to protect certain variable types. For example, it is illegal to copy anything but a
program to another program or a data variable to another data variable.
VarStore
must also insure that certain system variables are only stored to in the
proper mode. As an example,
tmin
which is used in parametric graphing, can
only be stored to in parametric graph mode and it has a limited range of values
that can be stored to it.
VarStore
does all of the necessary type and value
checking for all variables. To reiterate, the low-level routines do no type or value
checking and should be used with extreme caution.
Note:
Routines that take a variable number of arguments (
cmd_delvar
,
cmd_delfold
,
cmd_lock
,
cmd_unlock
,
cmd_archive
,
cmd_unarchiv
) require an END_TAG on the
estack to mark the end of the parameter list of variable names passed to them.
13.3.2. Storing and Retrieving Variable Data
As noted earlier, the file system is the preferred method for an app to store or
retrieve data.
VarStore
is the routine to store to a variable, and
VarRecall
is the
routine to access a variable. These routines are complicated because of the
built-in graphing application and the restrictions on the predefined system
variables. When a variable is accessed while graphing or building a table, a flag
in the symbol table entry for that variable is set. Whenever a store (or any
change, including delete, rename, etc.) is done to a variable that already exists,
the flags (one for each of the two possible graphs) must be checked to know if
the graph and table are now incorrect because the variable changed. Other
actions can also cause the graph or table to be incorrect — for example,
changing the angle mode or folder.
It is even more important to use
VarRecall
and
VarStore
for system variables,
some of which are not in the symbol table. In addition to the graph reference
flags, the type or range of a value must be checked before storing to some of the
system variables, and storing to some of them causes other system
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