1 Guidelines for Writing Empire Code
3 compiled and edited by Markus Armbruster
8 Empire is an old program, and the age shows in places. It took a lot
9 of people a lot of effort to write it. Chances are that some of them
10 were smarter than you and me. Treat the code with the respect it
13 These guidelines are just that: guidelines. Not law. There's no
14 Empire Coding Police. People hacked on Empire code long before I knew
15 it existed, and I hope they still will when I fade into Empire
16 history. But there's substantial experience behind these guidelines,
17 so don't dismiss them cavalierly.
19 Here's our goal: algorithmic clarity. All the rules and guidelines
20 are subservient to it. If you'd have to obfuscate your code to
21 satisfy the letter of some guideline, don't!
23 Mind, I said `clarity', not `self-realization' or `expression of your
24 individuality'. Dave Pare wrote:
26 Be invisible. When you make a change, think not about marking your
27 place in history, or about showing off how much nicer your two-space
28 tabs are than those old, icky eight-space tabs that the stupid
29 empire hackers of old used, but think instead about the aesthetics
30 of the whole. The resulting lines of code should flow smoothly from
31 the beginning of the procedure to the end. Empire is 60,000 lines
32 of code. If you're the general case, you're only changing fifty
33 lines, so be aware of that.
35 Some guidelines are more serious than others. When I use words like
36 `is', `shall' or `must', I mean it. When I write `should', it's a
39 Many guidelines concern style, i.e. they involve matters of taste.
40 That's how it has to be. Uniformity of style is important for
43 These guidelines don't attempt to be exhaustive. More complete
44 guidelines that are mostly compatible with Empire can be found at
45 http://www.jetcafe.org/~jim/c-style.html
48 Source tree organization
49 ------------------------
57 In My Egotistical Opinion, most people's C programs should be
58 indented six feet downward and covered with dirt."
61 Over the years, enough Empire coders lacked the good taste to preserve
62 the style of the original Empire code in their changes, and thus
63 turned the source code into an unreadable mess. In 2003, we fed it to
66 We tried to restore things to the original style, mostly. There is
67 one noteable change: basic indentation is now four spaces. Restoring
68 the original eight spaces would have resulted in many more long lines,
69 which would have to be broken by indent. Since indent isn't good at
70 breaking lines tastefully, we reluctantly chose four instead.
72 FIXME mention src/scripts/intend-emp, even better: convert it into an
73 indent profile and mention that.
75 If you use Emacs, `stroustrup' indentation style produces satisfactory
76 results. The command `c-set-style', normally bound to `C-c .', lets
77 you set the style for the current buffer. Set variable
78 `c-default-style' to "stroustrup" to switch to this style for all
83 Whether you use tab characters or not doesn't really matter that much,
84 but tab stops are every eight characters, period.
86 Indentation, placement of braces, function name
88 Basic indentation is four spaces. The opening brace goes on the same
89 line as `if', `struct', etc. Put `else' and do loops' `while' one the
90 same line as the closing brace. You are encouraged to leave out
91 syntactically optional braces. Don't indent case labels.
111 In a function definition, the return type, function name and the
112 braces must all start on a new line, unindented, like this:
120 This does not apply to function declarations.
124 Line length should not exceed 75 characters. Break such lines at a
125 logical place, preferably before an operator with low precedence.
126 Line up the continuation line with the innermost unclosed parenthesis,
127 if there is one, else indent it four spaces.
139 Use blank lines to separate different things. Functions must be
140 separated by a blank line. You are encouraged to insert a blank line
141 between a block's declarations and statements.
145 There is a space after `for', `if', and `while'. If `for' and `while'
146 are followed by `;' (empty loop body) on the same line, there is a
147 space before the `;'. There is no space between the function name and
148 the `(', but there is a space after each `,'. There should be no
149 space between type cast operator and operand. There is no extra space
150 after '(' and before ')'.
154 for (p = s; *p; ++p) ;
155 printf("%ld\n", (long)(p-s));
159 The function comment describing what a function does goes directly
160 above the definition.
162 Comments to the right of code should start in column 32 if possible
163 (counting from zero).
165 Comment lines should be indented exactly like the code the belong to.
167 You are encouraged to format multi-line comments like this:
170 * Please use complete sentences, with proper grammer,
171 * capitalization and puntuation. Use two spaces between
175 But please avoid elaborate boxes like this:
177 /***********************************************************
178 * Such decorations are a waste of time, hard to edit, and *
180 ***********************************************************/
182 Conditional compilation
184 Unless the conditional code is very short, please comment it like
203 DoNotUseStudlyCaps! Stick to lower_case and use underscores. Upper
204 case is for macros and enumeration constants.
206 File names should not differ in case only, since not all file systems
207 distinguish case. Best stick to lower case. Avoid funny characters
208 in file names. This includes space.
212 Like many good things, the preprocessor is best used sparingly.
213 Especially conditional compilation.
215 Do not use the preprocessor to `improve' the syntax of C!
217 Macro names should be ALL_CAPS to make them stand out. Otherwise,
218 they can be mistaken for objects or functions. This is bad, because
219 `interesting' behavior can hide inside macros, like not evaluating
220 arguments, or changing them. Exception: if a function-like macro
221 behaves exactly like a function, then you may use a lower case name.
223 Parameters that can take expression arguments must be parenthesized in
224 the expansion. If the expansion is an expression, it should be
225 parenthesized as well.
227 You are encouraged to use enumeration constants instead of macros when
228 possible. The existing code doesn't, but it makes sense all the same.
232 Every file should have a file comment FIXME
234 Every function should have a function comment that describes what it
235 does. FIXME elaborate. Writing such comments helps both future
236 maintainers and yourself: if it's too hard to write a concise function
237 comment, then your function is likely too complicated and could use a
240 The existing code has very little useful comments, and it'll likely
241 take us years to fix it. Please don't make it harder than it already
246 Do not declare system functions yourself; include the appropriate
249 Use prototypes, not old-style function declarations.
251 To get the best use of C's type checking, each function or variable
252 with external linkage should have exactly one declaration, in some
253 header file, and that declaration must be in scope at the definition.
254 No other declarations should exist. In particular, please include the
255 appropriate header instead of just declaring stuff again. The code
256 used to be full of this kind of junk, and it was quite some work to
259 Forward declarations of static functions should all go in one place
260 near the beginning of the file.
262 If you want a typedef name in addition to a structure or union tag,
263 give it the same name, like this:
265 typedef struct foo foo;
267 Yes, this is incompatble with C++. Reducing the number of names for
268 the same thing is more useful than compatibility to a programming
269 language we don't use.
271 Please don't hide away pointers with typedefs, like this:
273 typedef struct foo *foop;
275 When I see `foo *', I *know* what it is. When I see `foop', I have to
280 Casting pointers to and from `void *' clutters the code and serves no
281 purpose (repeat after me: C is not C++). It is also unsafe, because
282 the cast suppresses type warnings.
284 Casting function values to void clutters the code and serves little
285 purpose (repeat after me: C is not Pascal).
287 Casting an argument to the type of the parameter clutters the code and
288 serves no purpose (repeat after me: ISO C is not K&R C).
290 Factor out common code
292 Do not gratuitiously duplicate code! Ken Stevens said it well, and
293 it's as relevant as ever:
295 Cut-and-Paste coding is by far the biggest problem that the current
296 Empire suffers from. This is how cut-and-paste coding happens. Joe
297 Shmuck decides that he wants to add a new function to the server.
298 So he goes hunting through the server to find some already existing
299 code which does something similar to what he wants to do. This is
300 good. You should always write new code to imitate old code. What
301 is bad is when Joe Shmuck decides to simply "copy" 200 lines of code
302 from the old function into his new function, and then just change a
303 couple of little things here and there to suit his needs. This
304 method, known as Cut-and-Paste coding is the fastest and easiest way
305 to code. However, it results in a server that is impossible to
306 maintain. What Joe _should_ have done, is "move" the 200 lines of
307 code into a new _third_ function which the first two both call.
308 This is called writing a "general solution" to handle both cases.
309 Most of my work in the Empire2 project consisted in cleaning up
310 after a bunch of Joe Shmucks.
318 FIXME sizes, printf formats
322 FIXME conditional compilation is a last resort
332 Check error conditions meticulously. The existing code is bad enough
333 at this, please don't make it worse.
335 FIXME what to do on error
343 Empire uses non-preemptive threads: a thread runs until it yields the
344 processor. This simplifies programming, but there are still traps to
345 avoid. Empire threads may yield the processor whenever they do I/O or
348 Be careful with static storage. Read-only data is fine. More than
349 one thread writing static data is problematic, but there are safe
350 uses. For instance, a static scratch buffer that is never used across
353 Thread stacks cannot grow. If you use too much automatic storage, you
354 can overrun the stack with disastrous consequences. FIXME elaborate
356 Yielding the processor invalidates *all* the game state you copied
357 into variables. You have to reread and possibly recheck. See below.
361 Game state consists of several sets of objects, e.g. sectors, ships,
362 bmaps, ... Each set is fully held in memory and backed by a file in
365 There are several ways to access an object in set FOO:
367 * You can get a pointer to the object (not a copy!) with getFOOp().
369 This is inherently dangerous, because it allows you to update the
370 object in memory without updating the disk file. It's used mostly
371 in update code, where it pays major performance dividends, but there
372 are uses in other places. Whether they are wise is debatable.
374 Obviously, the object can change when you let another thread run.
375 This is not an issue in update code, because it never yields.
377 * You can get a copy with getFOO() and write it back with putFOO().
379 Yielding the processor invalidates the copy. In particular, if you
380 yield the processor between get and put, and another thread changes
381 the game data, then put will clobber that change, possibly resulting
384 Therefore, you have to re-get after a yield, and repeat any checks
385 you already made. If you can afford to bail out when something
386 changed at all, use check_FOO_ok().
388 Putting updates both the object in memory and the disk file.
390 If you write a function that takes a pointer to an object, think
391 twice before you put it, and if you do, mention it in the function
394 * Bmaps have special access functions.
396 Each country has to bmaps: the working bmap and the true bmap.
397 Unfortunately, the bmap code called the former `bmap' and the latter
400 You update bmaps with map_set(). This doesn't write through to the
401 file; instead, it returns non-zero when the update changed anything.
402 In that case, you must write bmaps to disk with writemap() before
403 you yield. If you only updated the working bmap, then you can call
410 Commit related changes together, unrelated changes separately.
412 See chapter Change Logs in the GNU coding standards for guidelines on
413 log messages. Try http://www.gnu.org/prep/standards_40.html#SEC40 or
414 search the web for `gnu coding standards change logs'.
416 Don't change whitespace gratuitiously, say just because your editor
417 screws up tabs. Such changes make it much harder to figure out who
418 changed what and when.
421 Historical guidelines, superseded by the above
424 Remarks from Dave Pare:
426 And now, a few editorial remarks on my views on Good Techniques for
427 Modifying Existing Software:
429 My safari through the hot and bug-ridden jungle that Empire has become
430 has given me some new insights on the modification of large software
431 packages. My adventure has prompted me to propose some simple coding
432 guidelines for those dreaming of hacking on the code:
434 1) Be invisible. When you make a change, think not about marking your
435 place in history, or about showing off how much nicer your two-space
436 tabs are than those old, icky eight-space tabs that the stupid empire
437 hackers of old used, but think instead about the asethetics of the whole.
438 The resulting lines of code should flow smoothly from the beginning of the
439 procedure to the end. Empire is 60,000 lines of code. If you're the
440 general case, you're only changing fifty lines, so be aware of that.
442 2) Procedurize. If you find yourself in a triple-nested loop, or a five
443 hundred line procedure, perhaps it's because you need to split some of
444 that code off into a procedure. In general, if you've got more than two
445 levels of tabs (or indentations), or more than one or two major loops in
446 a procedure, something may well be amiss.
449 Sasha Mikheev on indentation:
451 The empire indentation style can be achived by using
452 indent -orig -i8 foo.c
454 or in old c-mode emacs (versions before 19.29):
456 (setq c-indent-level 8)
457 (setq c-continued-statement-offset 8)
458 (setq c-argdecl-indent 8)
459 (setq c-brace-offset -8)
460 (setq c-label-offset -8)
463 Further comments by Ken Stevens:
466 The only variables which should be global are constants. If you write
467 a routine which changes a global variable, then you will corrupt the
468 data when two different players run that routine at the same time.
476 Should be rewritten as:
482 AIX has different conventions for signed chars, and IRIX requires the
483 /* comments */ after #endif.
486 Cut-and-Paste coding is by far the biggest problem that the current
487 Empire suffers from. This is how cut-and-paste coding happens. Joe
488 Shmuck decides that he wants to add a new function to the server. So
489 he goes hunting through the server to find some already existing code
490 which does something similar to what he wants to do. This is good.
491 You should always write new code to imitate old code. What is bad is
492 when Joe Shmuck decides to simply "copy" 200 lines of code from the old
493 function into his new function, and then just change a couple of
494 little things here and there to suit his needs. This method, known as
495 Cut-and-Paste coding is the fastest and easiest way to code. However,
496 it results in a server that is impossible to maintain. What Joe
497 _should_ have done, is "move" the 200 lines of code into a new _third_
498 function which the first two both call. This is called writing a
499 "general solution" to handle both cases. Most of my work in the
500 Empire2 project consisted in cleaning up after a bonch of Joe Shmucks.
501 I took repeated code and "consolidated" it into general function
505 Just to add to Dave's "Be Invisible" motto, I'd like to give a little
506 example to illustrate some basic do's and don'ts for coding style:
508 The following function has bad style:
510 double att_combat_eff(com,own)
515 if(com->type==EF_SECTOR)
519 str=com->sct_dcp->d_ostr;
521 str=com->sct_dcp->d_dstr;eff=2.0+(str-2.0)*eff;
522 }else if(com->type==EF_SHIP&&com->own!=own)
523 eff=(1.0+com->shp_mcp->m_armor/100.0);
526 Here is the same function written with "good" style:
529 att_combat_eff(com, own)
536 if (com->type == EF_SECTOR) {
537 eff = com->eff / 100.0;
539 str = com->sct_dcp->d_ostr;
541 str = com->sct_dcp->d_dstr;
542 eff = 2.0 + (str - 2.0) * eff;
543 } else if (com->type == EF_SHIP && com->own != own)
544 eff = (1.0 + com->shp_mcp->m_armor / 100.0);
549 These are all the things I fixed when changing the bad to the good:
550 - Function names should always start a new line (so you can search for them)
551 - There should always be a space after a ","
552 - Function arguments should be indented 8 spaces
553 - There should always be a tab after a type declaration
554 - Opening function bracket should be on a line by itself
555 - Indentation should be 8 spaces
556 - There should always be a space on both sides of every operator
557 - There should always be a space after if, for, while, switch
558 - The opening bracket should be on the same line as the if
559 - There should always be a space on either side of a {
560 - There should always be a new line after a ;
561 - The closing function bracket should be on a line by itself