Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Tue, 20 Mar 2012 17:58:29 +0100

Andrew Johnson wrote:

Hi Dirk,

Interesting, good detective work!

On 2012-03-20 Dirk Zimoch wrote:

In cac.cpp we find:
#define epicsAssertAuthor "Jeff Hill [email protected]"

But in templateInstances.cpp epicsAssertAuthor is not defined.

So does defining it there fix the problem?

- Andrew

It will remove the warning. But is that a fix?

Consider code where epicsAssertAuthor is A where the template is inlined

and B where the template is explicitly instantiated. Depending on the

Optimization flag, you get different behavior! Here, is it only a

message text, but it may be worse.

BEWARE: PHILOSOPHY!

It seems that using macros, including 'assert', in any inline code is

simply wrong programming. However, I cannot remember that I have ever

seen such a statement in any C++ book. It seems logical when you

consider what inline means and what macros are made for. They are simply

incompatible. But typically C++ books only say things like: "With C++

inline code, you don't need macros any more. Inline code is much better,

type safe, etc than macros." Unfortunately that is a lie. It is hard to

get inline code right and you cannot do everything with inline code that

you can do with macros.

Of course something like

template <class T>
T max(T a, T b) { return (a < b) ? b : a; }

is better than

#define max(a,b) ( (a) < (b) ? (b) : (a) )

when used in a context like max(getchar(), i++)

But often life is is more complicated than this.

Inline code is better than macros if you are a very experienced and

professional C++ programmer. Otherwise you will suffer from the one

million pitfalls in C++. And still you cannot do something like 'assert'

in C++ inline code.

END PHILOSOPHY.

Maybe this is the wrong part:

#ifndef epicsAssertAuthor
#   define epicsAssertAuthor 0
#endif

In base, only Jeff ever sets epicsAssertAuthor. So we can replace it

with a constant :-)

Dirk

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System