Re: Ahead of "main"?

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.
--
Flash Gordon
.

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