[GiNaC-list] Include Guards

[Chris Dams]

On Wed, 19 Jan 2005, I wrote:

> The simplest way is to just declare symbols in header files (i.e.,
> symbol x;) and to define them in one cpp-file (i.e., symbol x("x");). That
> is what I generally do. I am not a big fan of factories either.

Of course, I should have said "extern symbol x". However, using "extern ex
x;" in the header file and "ex x(symbol("x"));" in the cpp file is more
efficient.