Coding Style

In general, the ​coding standards used in the Linux kernel are versatile, comprehensive and quite good looking. They are boiling down to the following guide lines:

Indentation

Four spaces

Spaces

Spaces around keywords but not in inner parenthesis.

Brace placement

'{' at end of line except for function definition and '}' on its own line except in do-while-loops.

Naming

Descriptive for global functions and usually lower case with underscores.

Macros

Upper case for constants, lower case with underscores for macros resembling functions.

Structures

Consistency when using typedefs or not. For shared data structures reference counting should be implemented.

I would add the following:

Position of C-pointer star

At variable name not type.

const

Wherever possible.

White space

Avoid at all costs.

C99

Enable it and declare variables only when needed.

There are still some open questions:

• Number of newlines to separate functions?
• Comments: C vs. C++ style, usage of '*'?
• Alignment of multiple assignments?
• Breaking of long lines, especially argument lists?
• #define indentation? Commenting each #endif with the corresponding #define name makes the code hard to read in my opinion.
• Documentation tools? (​Doxygen, ​Sphinx, ​Natural Docs)
• Name prefixes? (e.g. 'g_' for global)

In essence, a bit of code would look like that:

#define PI 3.14159265
#define min(a,b) ((a) < (b) ? (a) : (b))

struct string {
    char *content;
    size_t length;
    int refcount;
};

struct string* clone_string(const char *s)
{
    if (s == NULL)
        return NULL;

    struct string *clone = (struct string *) malloc(sizeof(struct string));
    const int len = strlen(s);
    clone->content = (char *) malloc(len);
    clone->length = len;
    clone->refcount = 1;
    strncpy(clone->content, s, len);

    return clone;
}

Astyle Formatter

Corresponding flags for the ​astyle formatter are

astyle --style=k/r --indent=spaces --indent-switches --break-blocks --pad-oper --pad-header --delete-empty-lines --break-closing-brackets --align-pointer=name filename.c