use of define

Forum 2005-2010 (read only) Software Syntax & Programs
#1

I would like to set the size of array with a #define command.

It works like a charm when using this syntax :

#define test 8
int first[test][test];

But not at all when using it in a function :

#define test 8
int second(int parameter[test][test]) {}

The compilation failed and said : error: 'test' was not declared in this scop.

I do not unsterstand why. As the 2 dimensionnal array may vary from [8][8] to [20][70], I would like to save some memory at the compilation step.

Thanks for your help !

#2

Ah, you've hit on a weird quirk caused by one of the few manipulations we do to your code before passing it to the C/C++ compiler (avr-gcc). The Arduino software automatically generates prototypes for your functions. This basically involves taking a copy of the function header and sticking it at the top of your sketch. Unfortunately, this means that it ends up before the #define statement, and so test is undeclared at that point.

One workaround is to use a single dimensional array whose size is the product of the two dimensions you want, and use (y * X_SIZE + x) to access an element of it. Then you can declare the function as:

int second(int parameter[])

and not need to use the #define'd value.

#3

That's a bit tricky, but I will work. I can now finished to port a Game of Life on MAX7219.

#4