The Ten Commandments for C Programmers This is still wise counsel,
although many modern compilers
search out many of the same sins,
and there are often problems with
lint being aged and infirm, or una-
vailable in strange lands. There
are other tools, such as Saber C,
useful to similar ends.
``Frequently'' means thou shouldst
draw thy daily guidance from it,
rather than hoping thy code will
achieve lint's blessing by a sudden
act of repentance at the last
minute. De-linting a program which
has never been linted before is
often a cleaning of the stables
such as thou wouldst not wish on
thy worst enemies. Some observe,
also, that careful heed to the
words of lint can be quite helpful
in debugging.
``Study'' doth not mean mindless
zeal to eradicate every byte of
lint output-if for no other reason,
because thou just canst not shut it
up about some things-but that thou
should know the cause of its unhap-
piness and understand what worri-
some sign it tries to speak of.
2 Thou shalt not follow the NULL pointer, for chaos and
madness await thee at its end.
Clearly the holy scriptures were
mis-transcribed here, as the words
should have been ``null pointer'',
to minimize confusion between the
concept of null pointers and the
macro NULL (of which more anon).
Otherwise, the meaning is plain. A
null pointer points to regions
filled with dragons, demons, core
dumps, and numberless other foul
creatures, all of which delight in
frolicing in thy program if thou
disturb their sleep. A null
pointer doth not point to a 0 of
any type, despite some blasphemous
old code which impiously assumes
this.
3 Thou shalt cast all function arguments to the expected
type if they are not of that type already, even when
thou art convinced that this is unnecessary, lest they
take cruel vengeance upon thee when thou least expect
it.
A programmer should understand the
type structure of his language,
lest great misfortune befall him.
Contrary to the heresies espoused
by some of the dwellers on the
Western Shore, `int' and `long' are
not the same type. The moment of
their equivalence in size and
representation is short, and the
agony that awaits believers in
November 25, 1992
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their interchangeability shall last
forever and ever once 64-bit
machines become common.
Also, contrary to the beliefs com-
mon among the more backward inhabi-
tants of the Polluted Eastern
Marshes, `NULL' does not have a
pointer type, and must be cast to
the correct type whenever it is
used as a function argument.
(The words of the prophet Ansi,
which permit NULL to be defined as
having the type `void *', are oft
taken out of context and misunder-
stood. The prophet was granting a
special dispensation for use in
cases of great hardship in wild
lands. Verily, a righteous program
must make its own way through the
Thicket Of Types without lazily
relying on this rarely-available
dispensation to solve all its prob-
lems. In any event, the great
deity Dmr who created C hath wisely
endowed it with many types of
pointers, not just one, and thus it
would still be necessary to convert
the prophet's NULL to the desired
type.)
It may be thought that the radical
new blessing of ``prototypes''
might eliminate the need for cau-
tion about argument types. Not so,
brethren. Firstly, when confronted
with the twisted strangeness of
variable numbers of arguments, the
problem returns... and he who has
not kept his faith strong by
repeated practice shall surely fall
to this subtle trap. Secondly, the
wise men have observed that reli-
ance on prototypes doth open many
doors to strange errors, and some
indeed had hoped that prototypes
would be decreed for purposes of
error checking but would not cause
implicit conversions. Lastly,
reliance on prototypes causeth
great difficulty in the Real World
today, when many cling to the old
ways and the old compilers out of
desire or necessity, and no man
knoweth what machine his code may
be asked to run on tomorrow.
4 If thy header files fail to declare the return types of
thy library functions, thou shalt declare them thyself
with the most meticulous care, lest grievous harm
befall thy program.
The prophet Ansi, in her wisdom,
hath added that thou shouldst also
scourge thy Suppliers, and demand
on pain of excommunication that
they produce header files that
declare their library functions.
For truly, only they know the pre-
cise form of the incantation
appropriate to invoking their magic
in the optimal way.
The prophet hath also commented
that it is unwise, and leads one
into the pits of damnation and sub-
tle bugs, to attempt to declare
such functions thyself when thy
header files do the job right.
5 Thou shalt check the array bounds of all strings
(indeed, all arrays), for surely where thou typest
``foo'' someone someday shall type ``supercalifragilis-
ticexpialidocious''.
As demonstrated by the deeds of the
Great Worm, a consequence of this
commandment is that robust produc-
tion software should never make use
of gets(), for it is truly a tool
of the Devil. Thy interfaces
should always inform thy servants
of the bounds of thy arrays, and
servants who spurn such advice or
quietly fail to follow it should be
dispatched forthwith to the Land Of
Rm, where they can do no further
harm to thee.
6 If a function be advertised to return an error code in
the event of difficulties, thou shalt check for that
November 25, 1992
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code, yea, even though the checks triple the size of
thy code and produce aches in thy typing fingers, for
if thou thinkest ``it cannot happen to me'', the gods
shall surely punish thee for thy arrogance.
All true believers doth wish for a
better error-handling mechanism,
for explicit checks of return codes
are tiresome in the extreme and the
temptation to omit them is great.
But until the far-off day of
deliverance cometh, one must walk
the long and winding road with
patience and care, for thy Vendor,
thy Machine, and thy Software
delight in surprises and think
nothing of producing subtly mean-
ingless results on the day before
thy Thesis Oral or thy Big Pitch To
The Client.
Occasionally, as with the ferror()
feature of stdio, it is possible to
defer error checking until the end
when a cumulative result can be
tested, and this often produceth
code which is shorter and clearer.
Also, even the most zealous beli-
ever should exercise some judgement
when dealing with functions whose
failure is totally uninteresting...
but beware, for the cast to void is
a two-edged sword that sheddeth
thine own blood without remorse.
7 Thou shalt study thy libraries and strive not to re-
invent them without cause, that thy code may be short
and readable and thy days pleasant and productive.
Numberless are the unwashed heathen
who scorn their libraries on vari-
ous silly and spurious grounds,
such as blind worship of the Little
Tin God (also known as ``Effi-
ciency''). While it is true that
some features of the C libraries
were ill-advised, by and large it
is better and cheaper to use the
works of others than to persist in
re-inventing the square wheel. But
thou should take the greatest of
care to understand what thy
libraries promise, and what they do
not, lest thou rely on facilities
that may vanish from under thy feet
in future.
8 Thou shalt make thy program's purpose and structure
clear to thy fellow man by using the One True Brace
Style, even if thou likest it not, for thy creativity
is better used in solving problems than in creating
beautiful new impediments to understanding.
These words, alas, have caused some
uncertainty among the novices and
the converts, who knoweth not the
ancient wisdoms. The One True
Brace Style referred to is that
demonstrated in the writings of the
First Prophets, Kernighan and
Ritchie. Often and again it is
criticized by the ignorant as hard
to use, when in truth it is merely
somewhat difficult to learn, and
thereafter is wonderfully clear and
obvious, if perhaps a bit sensitive
to mistakes.
While thou might think that thine
own ideas of brace style lead to
clearer programs, thy successors
will not thank thee for it, but
rather shall revile thy works and
curse thy name, and word of this
might get to thy next employer.
Many customs in this life persist
because they ease friction and pro-
mote productivity as a result of
universal agreement, and whether
they are precisely the optimal
choices is much less important. So
it is with brace style.
As a lamentable side issue, there
has been some unrest from the
fanatics of the Pronoun Gestapo
over the use of the word ``man'' in
this Commandment, for they believe
that great efforts and loud shout-
ing devoted to the ritual
November 25, 1992
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purification of the language will
somehow redound to the benefit of
the downtrodden (whose real and
grievous woes tendeth to get lost
amidst all that thunder and fury).
When preaching the gospel to the
narrow of mind and short of temper,
the word ``creature'' may be sub-
stituted as a suitable pseudoBibli-
cal term free of the taint of Pol-
itical Incorrectness.
9 Thy external identifiers shall be unique in the first
six characters, though this harsh discipline be irksome
and the years of its necessity stretch before thee
seemingly without end, lest thou tear thy hair out and
go mad on that fateful day when thou desirest to make
thy program run on an old system.
Though some hasty zealots cry ``not
so; the Millenium is come, and this
saying is obsolete and no longer
need be supported'', verily there
be many, many ancient systems in
the world, and it is the decree of
the dreaded god Murphy that thy
next employment just might be on
one. While thou sleepest, he plot-
teth against thee. Awake and take
care.
It is, note carefully, not neces-
sary that thy identifiers be lim-
ited to a length of six characters.
The only requirement that the holy
words place upon thee is uniqueness
within the first six. This often
is not so hard as the belittlers
claimeth.
10 Thou shalt foreswear, renounce, and abjure the vile
heresy which claimeth that ``All the world's a VAX'',
and have no commerce with the benighted heathens who
cling to this barbarous belief, that the days of thy
program may be long even though the days of thy current
machine be short.
This particular heresy bids fair to
be replaced by ``All the world's a
Sun'' or ``All the world's a 386''
(this latter being a particularly
revolting invention of Satan), but
the words apply to all such without
limitation. Beware, in particular,
of the subtle and terrible ``All
the world's a 32-bit machine'',
which is almost true today but
shall cease to be so before thy
resume grows too much longer.
