This set of standards is designed to make our lives easier. It is developed with the simple goal of helping us keep the "new and improved Privoxy" consistent and reliable. Thus making maintenance easier and increasing chances of success of the project.
And that of course comes back to us as individuals. If we can increase our development and product efficiencies then we can solve more of the request for changes/improvements and in general feel good about ourselves. ;->
Explanation:
Comment as much as possible without commenting the obvious. For example do not comment "variable_a is equal to variable_b". Instead explain why variable_a should be equal to the variable_b. Just because a person can read code does not mean they will understand why or what is being done. A reader may spend a lot more time figuring out what is going on when a simple comment or explanation would have prevented the extra research. Please help your fellow Privoxy developers out!
The comments will also help justify the intent of the code. If the comment describes something different than what the code is doing then maybe a programming error is occurring.
Example:
/* if page size greater than 1k ... */
if (page_length() > 1024)
{
... "block" the page up ...
}
/* if page size is small, send it in blocks */
if (page_length() > 1024)
{
... "block" the page up ...
}
This demonstrates 2 cases of "what not to do". The first is a
"syntax comment". The second is a comment that does not fit what
is actually being done. |
Explanation:
Comments can help or they can clutter. They help when they are differentiated from the code they describe. One line comments do not offer effective separation between the comment and the code. Block identifiers do, by surrounding the code with a clear, definable pattern.
Example:
/*********************************************************************
* This will stand out clearly in your code!
*********************************************************************/
if (this_variable == that_variable)
{
do_something_very_important();
}
/* unfortunately, this may not */
if (this_variable == that_variable)
{
do_something_very_important();
}
if (this_variable == that_variable) /* this may not either */
{
do_something_very_important();
} |
Exception:
If you are trying to add a small logic comment and do not wish to "disrupt" the flow of the code, feel free to use a 1 line comment which is NOT on the same line as the code.
Explanation:
It goes back to the question of readability. If the comment is on the same line as the code it will be harder to read than the comment that is on its own line.
There are three exceptions to this rule, which should be violated freely and often: during the definition of variables, at the end of closing braces, when used to comment parameters.
Example:
/*********************************************************************
* This will stand out clearly in your code,
* But the second example won't.
*********************************************************************/
if (this_variable == this_variable)
{
do_something_very_important();
}
if (this_variable == this_variable) /*can you see me?*/
{
do_something_very_important(); /*not easily*/
}
/*********************************************************************
* But, the encouraged exceptions:
*********************************************************************/
int urls_read = 0; /* # of urls read + rejected */
int urls_rejected = 0; /* # of urls rejected */
if (1 == X)
{
do_something_very_important();
}
short do_something_very_important(
short firstparam, /* represents something */
short nextparam /* represents something else */ )
{
...code here...
} /* -END- do_something_very_important */ |
Explanation:
Logical steps should be commented to help others follow the intent of the written code and comments will make the code more readable.
If you have 25 lines of code without a comment, you should probably go back into it to see where you forgot to put one.
Most "for", "while", "do", etc... loops _probably_ need a comment. After all, these are usually major logic containers.
Explanation:
A reader of the code should be able to look at the comments just prior to the beginning of a function and discern the reason for its existence and the consequences of using it. The reader should not have to read through the code to determine if a given function is safe for a desired use. The proper information thoroughly presented at the introduction of a function not only saves time for subsequent maintenance or debugging, it more importantly aids in code reuse by allowing a user to determine the safety and applicability of any function for the problem at hand. As a result of such benefits, all functions should contain the information presented in the addendum section of this document.
Explanation:
Each closing brace should be followed on the same line by a comment that describes the origination of the brace if the original brace is off of the screen, or otherwise far away from the closing brace. This will simplify the debugging, maintenance, and readability of the code.
As a suggestion , use the following flags to make the comment and its brace more readable:
use following a closing brace: } /* -END- if() or while () or etc... */
Example:
if (1 == X)
{
do_something_very_important();
...some long list of commands...
} /* -END- if x is 1 */
or:
if (1 == X)
{
do_something_very_important();
...some long list of commands...
} /* -END- if (1 == X) */ |
Explanation:
Use all lowercase, and separate words via an underscore ('_'). Do not start an identifier with an underscore. (ANSI C reserves these for use by the compiler and system headers.) Do not use identifiers which are reserved in ANSI C++. (E.g. template, class, true, false, ...). This is in case we ever decide to port Privoxy to C++.
Example:
int ms_iis5_hack = 0; |
Instead of:
int msiis5hack = 0; int msIis5Hack = 0; |
Explanation:
Use all lowercase, and separate words via an underscore ('_'). Do not start an identifier with an underscore. (ANSI C reserves these for use by the compiler and system headers.) Do not use identifiers which are reserved in ANSI C++. (E.g. template, class, true, false, ...). This is in case we ever decide to port Privoxy to C++.
Example:
int load_some_file(struct client_state *csp) |
Instead of:
int loadsomefile(struct client_state *csp) int loadSomeFile(struct client_state *csp) |
Explanation:
Use a descriptive parameter name in the function prototype in header files. Use the same parameter name in the header file that you use in the c file.
Example:
(.h) extern int load_aclfile(struct client_state *csp); (.c) int load_aclfile(struct client_state *csp) |
Instead of:
(.h) extern int load_aclfile(struct client_state *); or (.h) extern int load_aclfile(); (.c) int load_aclfile(struct client_state *csp) |
Explanation:
Use all capital letters, with underscores between words. Do not start an identifier with an underscore. (ANSI C reserves these for use by the compiler and system headers.)
Example:
(enumeration) : enum Boolean {FALSE, TRUE};
(#define) : #define DEFAULT_SIZE 100; |
Note: We have a standard naming scheme for #defines that toggle a feature in the preprocessor: FEATURE_>, where > is a short (preferably 1 or 2 word) description.
Example:
#define FEATURE_FORCE 1 #ifdef FEATURE_FORCE #define FORCE_PREFIX blah #endif /* def FEATURE_FORCE */ |
Explanation:
Spell common words out entirely (do not remove vowels).
Use only widely-known domain acronyms and abbreviations. Capitalize all letters of an acronym.
Use underscore (_) to separate adjacent acronyms and abbreviations. Never terminate a name with an underscore.
Example:
#define USE_IMAGE_LIST 1 |
Instead of:
#define USE_IMG_LST 1 or #define _USE_IMAGE_LIST 1 or #define USE_IMAGE_LIST_ 1 or #define use_image_list 1 or #define UseImageList 1 |
Explanation:
The brace needs to be on a line all by itself, not at the end of the statement. Curly braces should line up with the construct that they're associated with. This practice makes it easier to identify the opening and closing braces for a block.
Example:
if (this == that)
{
...
} |
Instead of:
if (this == that) { ... }
or
if (this == that) { ... }
Note: In the special case that the if-statement is inside a loop, and it is trivial, i.e. it tests for a condition that is obvious from the purpose of the block, one-liners as above may optically preserve the loop structure and make it easier to read.
Status: developer-discretion.
Example exception:
while (more lines are read)
{
/* Please document what is/is not a comment line here */
if (it's a comment) continue;
do_something(line);
} |
Explanation:
Using braces to make a block will make your code more readable and less prone to error. All control statements should have a block defined.
Example:
if (this == that)
{
do_something();
do_something_else();
} |
Instead of:
if (this == that) do_something(); do_something_else();
or
if (this == that) do_something();
Note: The first example in "Instead of" will execute in a manner other than that which the developer desired (per indentation). Using code braces would have prevented this "feature". The "explanation" and "exception" from the point above also applies.
Example:
structure->flag = (condition); |
Instead of:
if (condition) { structure->flag = 1; } else { structure->flag = 0; }
Note: The former is readable and concise. The later is wordy and inefficient. Please assume that any developer new to the project has at least a "good" knowledge of C/C++. (Hope I do not offend by that last comment ... 8-)
Explanation:
Make it readable. The notable exception to using white space freely is listed in the next guideline.
Example:
int first_value = 0; int some_value = 0; int another_value = 0; int this_variable = 0; |
Explanation:
- structure pointer operator ( "->" ) - member operator ( "." ) - functions and parentheses
It is a general coding practice to put pointers, references, and function parentheses next to names. With spaces, the connection between the object and variable/function name is not as clear.
Example:
a_struct->a_member; a_struct.a_member; function_name(); |
Instead of: a_struct -> a_member; a_struct . a_member; function_name ();
Example:
int function1( ... )
{
...code...
return(ret_code);
} /* -END- function1 */
int function2( ... )
{
} /* -END- function2 */ |
Instead of:
int function1( ... ) { ...code... return(ret_code); } int function2( ... ) { }
Note: Use 1 blank line before the closing brace and 2 lines afterward. This makes the end of function standout to the most casual viewer. Although function comments help separate functions, this is still a good coding practice. In fact, I follow these rules when using blocks in "for", "while", "do" loops, and long if {} statements too. After all whitespace is free!
Status: developer-discretion on the number of blank lines. Enforced is the end of function comments.
Explanation:
If some use 8 character TABs and some use 3 character TABs, the code can look *very* ragged. So use 3 character indentions only. If you like to use TABs, pass your code through a filter such as "expand -t3" before checking in your code.
Example:
static const char * const url_code_map[256] =
{
NULL, ...
};
int function1( ... )
{
if (1)
{
return ALWAYS_TRUE;
}
else
{
return HOW_DID_YOU_GET_HERE;
}
return NEVER_GETS_HERE;
} |
Explanation:
Do not assume that the variables declared will not be used until after they have been assigned a value somewhere else in the code. Remove the chance of accidentally using an unassigned variable.
Example:
short a_short = 0; float a_float = 0; struct *ptr = NULL; |
Note: It is much easier to debug a SIGSEGV if the message says you are trying to access memory address 00000000 and not 129FA012; or array_ptr[20] causes a SIGSEV vs. array_ptr[0].
Status: developer-discretion if and only if the variable is assigned a value "shortly after" declaration.
Explanation:
Value should be phrased as a question that would logically be answered as a true or false statement
Example:
should_we_block_this(); contains_an_image(); is_web_page_blank(); |
Explanation:
The default return for a function is an int. To avoid ambiguity, create a return for a function when the return has a purpose, and create a void return type if the function does not need to return anything.
Explanation:
It is easy to write the following code, and a clear argument can be made that the code is easy to understand:
Example:
for (size_t cnt = 0; cnt < block_list_length(); cnt++)
{
....
} |
Note: Unfortunately, this makes a function call for each and every iteration. This increases the overhead in the program, because the compiler has to look up the function each time, call it, and return a value. Depending on what occurs in the block_list_length() call, it might even be creating and destroying structures with each iteration, even though in each case it is comparing "cnt" to the same value, over and over. Remember too - even a call to block_list_length() is a function call, with the same overhead.
Instead of using a function call during the iterations, assign the value to a variable, and evaluate using the variable.
Example:
size_t len = block_list_length();
for (size_t cnt = 0; cnt < len; cnt++)
{
....
} |
Exceptions: if the value of block_list_length() *may* change or could *potentially* change, then you must code the function call in the for/while loop.
Explanation:
This allows a developer to define a const pointer and call your function. If your function does not have the const keyword, we may not be able to use your function. Consider strcmp, if it were defined as: extern int strcmp(char *s1, char *s2);
I could then not use it to compare argv's in main: int main(int argc, const char *argv[]) { strcmp(argv[0], "privoxy"); }
Both these pointers are *const*! If the c runtime library maintainers do it, we should too.
Explanation:
Most structures cannot fit onto a normal stack entry (i.e. they are not 4 bytes or less). Aka, a function declaration like: int load_aclfile(struct client_state csp)
would not work. So, to be consistent, we should declare all prototypes with "pass by value": int load_aclfile(struct client_state *csp)
Explanation:
Your include statements should contain the file name without a path. The path should be listed in the Makefile, using -I as processor directive to search the indicated paths. An exception to this would be for some proprietary software that utilizes a partial path to distinguish their header files from system or other header files.
Example:
#include <iostream.h> /* This is not a local include */ #include "config.h" /* This IS a local include */ |
Exception:
/* This is not a local include, but requires a path element. */ #include <sys/fileName.h> |
Note: Please! do not add "-I." to the Makefile without a _very_ good reason. This duplicates the #include "file.h" behavior.