AKMA’s Random Thoughts

much appreciated...

We can see an example of this in our code we've written so far. In each function's block, we declare variables that hold our data. When each function ends, the variables within are disposed of, and the space they were using is given back to the computer to use. The variables live in the blocks of conditionals and loops we write, but they don't cascade into functions we call, because those aren't sub-blocks, but different sections of code entirely. Every variable we've written has a well-defined lifetime of one function.

This code should compile and run just fine, and you should see no changes in how the program works. So why did we do all of that?

This is another function provided for dealing with the heap. After you've created some space in the Heap, it's yours until you let go of it. When your program is done using it, you have to explicitly tell the computer that you don't need it anymore or the computer will save it for your future use (or until your program quits, when it knows you won't be needing the memory anymore). The call to simply tells the computer that you had this space, but you're done and the memory can be freed for use by something else later on.

Seth Roby graduated in May of 2003 with a double major in English and Computer Science, the Macintosh part of a three-person Macintosh, Linux, and Windows graduating triumvirate.

This is another function provided for dealing with the heap. After you've created some space in the Heap, it's yours until you let go of it. When your program is done using it, you have to explicitly tell the computer that you don't need it anymore or the computer will save it for your future use (or until your program quits, when it knows you won't be needing the memory anymore). The call to simply tells the computer that you had this space, but you're done and the memory can be freed for use by something else later on.

Inside each stack frame is a slew of useful information. It tells the computer what code is currently executing, where to go next, where to go in the case a return statement is found, and a whole lot of other things that are incredible useful to the computer, but not very useful to you most of the time. One of the things that is useful to you is the part of the frame that keeps track of all the variables you're using. So the first place for a variable to live is on the Stack. This is a very nice place to live, in that all the creation and destruction of space is handled for you as Stack Frames are created and destroyed. You seldom have to worry about making space for the variables on the stack. The only problem is that the variables here only live as long as the stack frame does, which is to say the length of the function those variables are declared in. This is often a fine situation, but when you need to store information for longer than a single function, you are instantly out of luck.