If you start a new file, you get to choose the style.
If you change an existing file, follow the existing style.

Hard tabs are OK, as long as you consider the tab stops to
be every 8 characters. You can also use 2, 3, or 4 spaces.
Tabs are kind of yucky, since cut-and-paste mangles them
sometimes and they make "diff -Naurd old new" output less
readable.

Spaces within a line don't matter much, and won't be
considered part of the style. Just make it readable:

if(x){            // OK
if( x ){           // OK
if (x) {            // OK
if(x==y && a==b){     // OK
if(x == y && a == b){ // poor
if(x==y&&a==b){       // poor

This is evil:

szWinStallman
FoulCodingStyle (int iInsanity)
  {
     if (iInsanity)
       {
          GoHackEmacs () ;
       }
          else
       {
          SeekHelpForYourLisp () ;
       }
  }


Curly braces belong at the end of a line. If you must, go ahead
and make function bodies an exception to that rule. (as Linus does)

Big fprintf() calls and similar go like this:

fprintf(fd, "%d %d %d %d %d %d\n",
  sdfsdf_sdfsdf + sdfs_iii,     // not an example of good names!
  iijjij,
  kjfkkj_sdfssss_sfff,
  sdflkjfdskj + sdf - sfds,
  jksss,
  sfssss + wwwwfwfw
);

Keep these distinct: NULL, '\0', 0, 0.0

Command-line parsers need to be bomb-proof. It is not acceptable
to crash due to a messed up command-line. For an option "-x" that
takes an argument, accept both "-x arg" and "-xarg". Remember to
support "--" and "--version".

Be extremely careful when handling data from other users.
For example, it is a security hole if /proc/123/cmdline can
overflow an array. It is often a security hole if you allow
non-ASCII characters to be printed. Assuming the console is
not in UTF-8 mode, all of these are bad: "\b\e\f\n\r\t\v\x9b".
(the "\x9b" is valid in UTF-8 mode, but equivalent to "\e["
when not in UTF-8 mode -- which gives control of terminal
settings) It's best if you consider user-supplied data to
be unsafe, since this makes for less work in case the code
ends up needing to run setuid. Termcap data is user-supplied.
Except for the above security issues, don't bother to check
for something you can't handle... like printf() failing.
It is expected that /dev exists and so on.

Remember that a read() may return early, with partial data
or with -1 and errno set to EINTR. You then must try again.

char:      may be signed or unsigned by default
int:       always 32-bit
long long: always 64-bit
pointer:   either 32-bit or 64-bit
long:      same size as a pointer
KLONG:     same size as a pointer or long IN THE KERNEL

Functions used in just one file must be marked static.
Use the "const" and "restrict" keywords wherever you can.

Put main() at the bottom of a file so you don't need all
those ugly forward declarations.

Avoid the strcat() function. It is slow. For some odd
reason, snprintf() is faster than sprintf().

Reuse memory allocations when you can. When using realloc(),
do your increments by more than one. 25% is a nice amount.

Avoid compile-time choices. They make documentation difficult,
and they are not friendly to binary distribution.

Write programs that can handle a million processes without
getting hopelessly slow. Allow for /proc/123/cmdline to
be at least 128 kB.

The LGPL license is strongly preferred. This allows use of
the code in the library.