classes memory cost

[z3ngew]

Hello everyone,
I have a little question, if i intended to use classes in writing a program, i would like to know, if the memory cost is being paid for the overall class(it is stored in memory typedef) or only the methods and variables being used are paid for.

Thanks in advance,
z3ngew

[temtronic]

quick,simple answer

cut some code and read the listings.
you'ld have to supply us with a good test program to play with....

Honestly, ask 2 programmers to cut code and you'll get 3 ways to do it!

Without a baseline test program,who can really say? And..if the 'cost' is just a few bytes, who cares? Just buy a bigger PIC ! That's been the PC program philosophy for decades.memory is cheap,cut lousy code, crank up the clock speed, it 'works'....


jay

[RF_Developer]

[z3ngew]

thanks for the reply temtronic
but, i haven't started with the code just yet, but i was wondering which one to choose, a class structure or a simple c source file and include it.

so class structure will give you a good control of your code but, is it really worth it, or just it will eat all my device memory?

Thank you,
z3ngew

[z3ngew]

RF_Developer you are correct, i am writing something approaching class-like code in C it is mainly based on struct data structure.

I want to know if all the approached_class will be counted as memory using or just the used methods and variables,

Thanks in advance,
z3ngew

[jeremiah]

The CCS compiler won't generate code for functions that you do not use (if you use function pointers, merely assigning a function to a function pointer does count as "use"). It will take RAM for any variables you create regardless if you use them or not (mind you typedef does not create anything, so merely typdef'ing out a struct for your class won't produce any code).

In terms of extra memory generated by trying to implement class like structs in functions, you will probably get a little more memory generated, but the how much and what type depends on the implemenation. For example, say you try and implement the hidden *this pointer in your functions:

void myClassFunction(class_type *this, int param1, int param2, ...);

In this case, you will at the least generate extra ROM instructions to de-reference the pointer each time you use the struct in the function and lose a little time de-referencing it each time. In most cases you will also use an extra RAM variable for the function call, but only as much as the size of your pointer.

If you use the reference method, it is a little different:

void myClassFunction(class_type &o, int param1, int param2, ...);

This method will most often cause CCS to inline the function. This will mean more ROM instructions overall, but won't take any extra RAM (when passed with &, CCS tries to directly address memory) and you won't lose time in the function de-referencing the pointer since it will be directly using the memory address. I like this method better, especially on a PIC with 32k+ ROM.

There are other ways, but that is just a little off the top of my head.

[z3ngew]

Thanks for the explanation my friend