Texas Instruments TI89 Developer Guide - Page 179

Chapter 13: Memory Management 137 push_setfold TokenizeSymName VarRecall - Set current default folder (TI-BASIC version of FolderCur). - Tokenize a name and check for invalid or reserved names. - 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 TI-89 / TI-92 Plus Developer Guide Not for Distribution Beta Version January 26, 2001