TIC's pointer type

Pointers in TIC have some properties of ANSI C pointers, but there's enough difference that you should probably read this no matter how pointer-experienced you think you are.

First of all, here's what a pointer is... A "pointer" is simply an index into a lookup-table. In that table are "actual" pointers to the memory blocks. The reason you want to access memory via this table is that the TI operating system moves data around quite frequently, and this table keeps track of these data moves. The point is, if you type, for example, x=malloc(2568);, 2568 bytes of consecutive memory will be allocated to you (if it's available) and the address of the beginning of that array will be stored into the lookup-table. Then your variable x will contain an index into that lookup-table. Let's say that when the memory was allocated, there were already 52 chunks allocated (by other parts of your program, or by the operating system), well then, the pointer to the beginning of that chunk would be in the 53rd location in the allocation lookup-table, and your variable x would then contain the number 53.

Using this lookup-table and some tricks, you can create arbitrarily- complex data sructures... here's how...

to allocate a certain amount of memory and "call it" x, type...

x=malloc(size); This statement will allocate size number of bytes in RAM (remember, if you want enough space for 100 int's, you need to allocate 400 bytes!!! -- remember, 1 int = 4 bytes), then it will store the index number of that block in the lookup-table into x.

To use some value in this block, just use standard "array-accessing" syntax...

y=x[8]; A similar syntax is used for storing to the array...

array1[10]=5; Using all of these features, you can easily make multi-dimentional arrays... To do it, you can just make an array of pointers to arrays. This is TIC's multidimentional-array convention, which conforms to the ANSI-C convention. Here's how do set it up...

/* creating a 5x12 array... */ int XDim=5; int YDim=12; int 2dArray; /* setup base-level array... */ 2dArray=malloc(4*XDim); /* setup 2nd-dimension of array */ for( i=0 ; i 2dArray[i]=malloc(4*YDim); the TIC compiler will understand the following code...

element=2dArray[3][9]; Remember that array index counting starts at zero!

Before leaving your program, you should de-allocate the memory you used, that is, "give it back" to your TI's operating system. To do this, use the free() function... /* deleting a 5x12 array... */ /* delete 2nd-level memory blocks */ for( i=0 ; i free(2dArray[i]); /* delete base-level array... */ free(2dArray); (For a "real-life" example of this idea, see the Minesweeper game, mine.tic).

Of course, you could leave those blocks in the RAM-memory, but unless they're being pointed to by "constant" variabls, you won't know where they've went to, so BEWARE when trying this. If you DO do this, it will just "use up" extra memory. This memory is recorded as memory in the SYSTEM listing on your TI's MEM menu. This is ok if you keep track of it for later use... Version 0.7 Beta of TICC will have an option to "clean up" after your program is done, that is, to have all of your allocated memory be automatically deleted.

If you run across an error in allocating memory (such as not having enough memory at the time of a call to malloc()), the program will stop with a display screen saying that you've run out of memory. If you want the program to do something else (like clean up some things, or give your own error message), you can just define a procedure, called mallocerr(), that will be run instead of the default error handler. Here's an example...

int Array; int ValidMem; proc main() { ValidMem=1; Array=malloc(10); if( ValidMem ) DoGame(); else Fail(); }main; proc mallocerr() { ValidMem=0; }mallocerr; ...this will allow you to give the user an out-of-memory message (the Fail() function) if there is not enough memory instead of just stopping with our ugly default out-of-memory handler...

Well, that is kindof the whole story on TIC's arrays... If you have any questions, feel free to mail us.