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uGFX coding style
This is a short document describing the preferred coding style for uGFX.
Chapter 1: Indentation
Tabs are 4 characters, and thus indentations are also 4 characters.
Rationale: We like 4 character tabs much better than 8 character tabs.
It is more readable.
Chapter 2: Placing Braces
The preferred way, as shown to us by the prophets Kernighan and Ritchie,
is to put the opening brace last on the line, and put the closing brace first,
thusly:
if (x is true) {
we do y
}
However, there is one special case, namely functions: they have the
opening brace at the beginning of the next line, thus:
int function(int x)
{
body of function
}
We will however accept braces in the general block style for functions
but not the other way around. General blocks MUST have their opening brace
on the same line as the conditional statement.
Note that the closing brace is empty on a line of its own, _except_ in
the cases where it is followed by a continuation of the same statement,
ie a "while" in a do-statement or an "else" in an if-statement, like
this:
do {
body of do-loop
} while (condition);
and
if (x == y) {
..
} else if (x > y) {
...
} else {
....
}
Note that closing brace is indented to the level of the start of the block.
Structure definitions are an optional exception. Both of the below style are
acceptable:
typedef struct {
int a;
...
} mytype;
struct mystruct {
int a;
...
}
Chapter 3: Naming
C is a Spartan language, and so should your naming be. Unlike Modula-2
and Pascal programmers, C programmers do not use cute names like
ThisVariableIsATemporaryCounter. A C programmer would call that
variable "tmp", which is much easier to write, and a lot less
difficult to understand.
HOWEVER, while long mixed-case names are frowned upon, descriptive names for
global variables are a must. To call a global function "foo" is a
shooting offense.
GLOBAL variables (to be used only if you _really_ need them) need to
have descriptive names, as do global functions. If you have a function
that counts the number of active users, you should call that
"countActiveUsers()" or similar, you should _not_ call it "cntusr()".
WHERE long names are required as described above, we prefer the use of
capitalisation on subsequent words (but not the first) rather than underscores
to seperate the words. For example "countActiveUsers()" is preferred to
"count_active_users()" as it is at least as readable and is shorter.
Encoding the type of a function into the name (so-called Hungarian
notation) is brain damaged - the compiler knows the types anyway and can
check those, and it only confuses the programmer.
LOCAL variable names should be short, and to the point. If you have
some random integer loop counter, it should probably be called "i".
Calling it "loopCounter" is non-productive, if there is no chance of it
being mis-understood. Similarly, "tmp" can be just about any type of
variable that is used to hold a temporary value.
Chapter 4: Functions
Functions should be short and sweet, and do just one thing.
The maximum length of a function is inversely proportional to the
complexity and indentation level of that function. So, if you have a
conceptually simple function that is just one long (but simple)
case-statement, where you have to do lots of small things for a lot of
different cases, it's OK to have a longer function.
However, if you have a complex function, and you suspect that a
less-than-gifted first-year high-school student might not even
understand what the function is all about, you should adhere to the
maximum limits all the more closely. Use helper functions with
descriptive names (you can ask the compiler to in-line them if you think
it's performance-critical, and it will probably do a better job of it
that you would have done).
Another measure of the function is the number of local variables. They
shouldn't exceed 5-10, or you're possibly doing something wrong. Re-think the
function, and split it into smaller pieces. A human brain can
generally easily keep track of about 7 different things, anything more
and it gets confused. You need to understand what you did 2 weeks from now.
Because uGFX is intended for embedded platforms there are other considerations
that may cause exceptions or emphasise the above. For example, stack space is
a premium. This means that the number of local variables should be minimised as
should the number of parameters. Passing through multiple levels of functions
with lots of parameters is very bad indeed and this can override the desire to
keep functions short and sweet. Clarity however is still essential.
Chapter 5: Commenting
Comments are good, but there is also a danger of over-commenting. NEVER
try to explain HOW your code works in a comment: it's much better to
write the code so that the _working_ is obvious, and it's a waste of
time to explain badly written code. Generally, you want your comments to tell
WHAT your code does, not HOW.
We use doxygen to document the system. That means that most public functions
are documented in the header defintion file. We do not put doxygen comments in
the source file itself.
Within the source file, comments should be used to seperate blocks of functions
or definitions within the file. This is to provide clarity to the structure of
the source file itself. An example could be:
/***************************
* Drawing Functions
***************************/
Single line comments using "//" to start the comment should be used for just that
purpose, to assist in the understanding of that single line. Mutliple single line
comments should never be used to create a block comment. For example,
// This is a very long
// comment spanning several
// lines
is a very bad use of comments.
Comments within function bodies should be small comments to note or warn
about something particularly clever (or ugly), but try to avoid excess.
Instead, put the comments at the head of a block of code to explain the block
rather than a comment on each line.
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