Re: Ahead of "main"?

On Sun, 29 Apr 2007 23:48:23 +0100, Flash Gordon
<spam@xxxxxxxxxxxxxxxxxx> wrote:

Stephen Sprunk wrote, On 29/04/07 22:35:
"mdh" <mdeh@xxxxxxxxxxx> wrote in message
news:1177877117.874830.65670@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hi all,
Going quite methodically through K& R ( as some of you can attest
to!), I have never seen a big diffference in declaring a function
within "main" or "ahead" of it. Now, (p119, K&R II), the discussion
states that "functions "whatever" " should be declared ahead of
main.
Is there a good reason for this?

In Standard C, functions cannot be declared "within" main(); these are
called nested functions and are implemented as an extension by some
compilers, but in general you should never use them.

Wrong. They can be *declared* within main or any other function, they
just cannot be *defined* in a function. A declaration says something
exists, a definition says what it is, the difference is important in C.

Therefore, the
debate is about whether to declare functions before or after main().

As a rule, you should declare all functions before you call them; I
won't go into the reasons why, as Eric did a good job of that. One
style is to define all other functions before main(), which also
declares them. The other is to declare all of your functions in a group
near the beginning of the source, and then you can define them in any
order you want. The latter style is effectively required when you move
to multi-file projects, and the standard practice is to put all of your
function declarations in header (.h) files so that each source file can
simply #include the appropriate header files and then use whatever
functions are needed.

Actually, you should not put *all* your function definitions in header
files, since generally there are some which should be local to a given
source file and declared static in that source file. I.e. you should
always limit visibility to the smallest unit that makes sense, since
then you don't have to look as far to see all of the usage.

You should not put any function definitions in a header file. I would
go a step further and say no object definitions either. Only
declarations. The only definitions in a header file should be typedef
(oops, even though it is called a type definition in the standard, it
is specifically described as a declaration) and macro definitions.


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