Declare variable as locally as possible

Question

I'm new to Linux kernel development.

One thing that bothers me is a way a variables are declared and initialized.

I'm under impression that code uses variable declaration placement rules for C89/ANSI C (variables are declared at the beginning of block), while C99 relaxes the rule.

My background is C++ and there many advises from "very clever people" to declare variable as locally as possible - better declare and initialize in the same instruction:

• Google C++ Style Guide
• C++ Coding Standards: 101 Rules, Guidelines, and Best Practices - item 18
• A good discussion about it here.

What is the accepted way to initialize variables in Linux kernel?

Answer 1

I couldn't find a relevant passage in the Linux kernel coding style. So, follow the convention used in existing code -- declare variables at beginning of block -- or run the risk of your code seeming out-of-place.

Reasons why variables at beginning of block is a Good Thing:

• the target architecture may not have a C99 compiler
• ... can't think of more reasons

Answer 2

You should always try to declare variables as locally as possible. If you're using C++ or C99, that would usually be right before the first use.
In older C, doing that doesn't fall under "possible", and there the place to declare those variables would usually be the beginning of the current block.

(I say 'usually' because of some cases with functions and loops where it's better to make them a bit more global...)