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# PHP coding standards
This file lists several standards that any programmer adding or changing code in
PHP should follow. Since this file was added at a very late stage of the
development of PHP v3.0, the code base does not fully follow it, but new
features are going in that general direction. Many sections have been recoded to
use these rules.
## Code implementation
1. Document your code in source files and the manual. (tm)
2. Functions that are given pointers to resources should not free them.
For instance, `function int mail(char *to, char *from)` should NOT free to
and/or from.
Exceptions:
* The function's designated behavior is freeing that resource. E.g.
`efree()`
* The function is given a boolean argument, that controls whether or not the
function may free its arguments (if true - the function must free its
arguments, if false - it must not)
* Low-level parser routines, that are tightly integrated with the token
cache and the bison code for minimum memory copying overhead.
3. Functions that are tightly integrated with other functions within the same
module, and rely on each other non-trivial behavior, should be documented as
such and declared `static`. They should be avoided if possible.
4. Use definitions and macros whenever possible, so that constants have
meaningful names and can be easily manipulated. The only exceptions to this
rule are 0 and 1, when used as `false` and `true` (respectively). Any other
use of a numeric constant to specify different behavior or actions should be
done through a `#define`.
5. When writing functions that deal with strings, be sure to remember that PHP
holds the length property of each string, and that it shouldn't be
calculated with `strlen()`. Write your functions in such a way so that
they'll take advantage of the length property, both for efficiency and in
order for them to be binary-safe. Functions that change strings and obtain
their new lengths while doing so, should return that new length, so it
doesn't have to be recalculated with `strlen()` (e.g. `php_addslashes()`).
6. NEVER USE `strncat()`. If you're absolutely sure you know what you're doing,
check its man page again, and only then, consider using it, and even then,
try avoiding it.
7. Use `PHP_*` macros in the PHP source, and `ZEND_*` macros in the Zend part of
the source. Although the `PHP_*` macros are mostly aliased to the `ZEND_*`
macros it gives a better understanding on what kind of macro you're calling.
8. When commenting out code using a `#if` statement, do NOT use `0` only.
Instead use `"<git username here>_0"`. For example, `#if FOO_0`, where `FOO`
is your git user `foo`. This allows easier tracking of why code was
commented out, especially in bundled libraries.
9. Do not define functions that are not available. For instance, if a library is
missing a function, do not define the PHP version of the function, and do
not raise a run-time error about the function not existing. End users should
use `function_exists()` to test for the existence of a function.
10. Prefer `emalloc()`, `efree()`, `estrdup()`, etc. to their standard C library
counterparts. These functions implement an internal "safety-net" mechanism
that ensures the deallocation of any unfreed memory at the end of a request.
They also provide useful allocation and overflow information while running
in debug mode.
In almost all cases, memory returned to the engine must be allocated using
`emalloc()`.
The use of `malloc()` should be limited to cases where a third-party library
may need to control or free the memory, or when the memory in question needs
to survive between multiple requests.
## User functions/methods naming conventions
1. Function names for user-level functions should be enclosed with in the
`PHP_FUNCTION()` macro. They should be in lowercase, with words underscore
delimited, with care taken to minimize the letter count. Abbreviations
should not be used when they greatly decrease the readability of the
function name itself:
Good:
```php
str_word_count
array_key_exists
```
Ok:
```php
date_interval_create_from_date_string
// Could be 'date_intvl_create_from_date_str'?
get_html_translation_table()
// Could be 'html_get_trans_table'?
```
Bad:
```php
hw_GetObjectByQueryCollObj
pg_setclientencoding
jf_n_s_i
```
2. If they are part of a "parent set" of functions, that parent should be
included in the user function name, and should be clearly related to the
parent program or function family. This should be in the form of `parent_*`:
A family of `foo` functions, for example:
Good:
```php
foo_select_bar
foo_insert_baz
foo_delete_baz
```
Bad:
```php
fooselect_bar
fooinsertbaz
delete_foo_baz
```
3. Function names used by user functions should be prefixed with `_php_`, and
followed by a word or an underscore-delimited list of words, in lowercase
letters, that describes the function. If applicable, they should be declared
`static`.
4. Variable names must be meaningful. One letter variable names must be avoided,
except for places where the variable has no real meaning or a trivial
meaning (e.g. `for (i=0; i<100; i++) ...`).
5. Variable names should be in lowercase. Use underscores to separate between
words.
6. Method names follow the *studlyCaps* (also referred to as *bumpy case* or
*camel caps*) naming convention, with care taken to minimize the letter
count. The initial letter of the name is lowercase, and each letter that
starts a new `word` is capitalized:
Good:
```php
connect()
getData()
buildSomeWidget()
```
Bad:
```php
get_Data()
buildsomewidget()
getI()
```
7. Class names should be descriptive nouns in *PascalCase* and as short as
possible. Each word in the class name should start with a capital letter,
without underscore delimiters. The class name should be prefixed with the
name of the "parent set" (e.g. the name of the extension) if no namespaces
are used. Abbreviations and acronyms as well as initialisms should be
avoided wherever possible, unless they are much more widely used than the
long form (e.g. HTTP or URL). Abbreviations start with a capital letter
followed by lowercase letters, whereas acronyms and initialisms are written
according to their standard notation. Usage of acronyms and initialisms is
not allowed if they are not widely adopted and recognized as such.
Good:
```php
Curl
CurlResponse
HTTPStatusCode
URL
BTreeMap // B-tree Map
Id // Identifier
ID // Identity Document
Char // Character
Intl // Internationalization
Radar // Radio Detecting and Ranging
```
Bad:
```php
curl
curl_response
HttpStatusCode
Url
BtreeMap
ID // Identifier
CHAR
INTL
RADAR // Radio Detecting and Ranging
```
## Internal function naming conventions
1. Functions that are part of the external API should be named
`php_modulename_function()` to avoid symbol collision. They should be in
lowercase, with words underscore delimited. Exposed API must be defined in
`php_modulename.h`.
```c
PHPAPI char *php_session_create_id(PS_CREATE_SID_ARGS);
```
Unexposed module function should be static and should not be defined in
`php_modulename.h`.
```c
static int php_session_destroy()
```
2. Main module source file must be named `modulename.c`.
3. Header file that is used by other sources must be named `php_modulename.h`.
## Syntax and indentation
1. Never use C++ style comments (i.e. `//` comment). Always use C-style comments
instead. PHP is written in C, and is aimed at compiling under any ANSI-C
compliant compiler. Even though many compilers accept C++-style comments in
C code, you have to ensure that your code would compile with other compilers
as well. The only exception to this rule is code that is Win32-specific,
because the Win32 port is MS-Visual C++ specific, and this compiler is known
to accept C++-style comments in C code.
2. Use K&R-style. Of course, we can't and don't want to force anybody to use a
style he or she is not used to, but, at the very least, when you write code
that goes into the core of PHP or one of its standard modules, please
maintain the K&R style. This applies to just about everything, starting with
indentation and comment styles and up to function declaration syntax. Also
see [Indentstyle](http://www.catb.org/~esr/jargon/html/I/indent-style.html).
3. Be generous with whitespace and braces. Keep one empty line between the
variable declaration section and the statements in a block, as well as
between logical statement groups in a block. Maintain at least one empty
line between two functions, preferably two. Always prefer:
```c
if (foo) {
bar;
}
```
to:
```c
if(foo)bar;
```
4. When indenting, use the tab character. A tab is expected to represent four
spaces. It is important to maintain consistency in indenture so that
definitions, comments, and control structures line up correctly.
5. Preprocessor statements (`#if` and such) MUST start at column one. To indent
preprocessor directives you should put the `#` at the beginning of a line,
followed by any number of whitespace.
## Testing
1. Extensions should be well tested using `*.phpt` tests. Read about that at
[qa.php.net](https://qa.php.net/write-test.php) documentation.
## Folding hooks
Use `{{{` symbols for the folding mode in Emacs and vim (`set fdm=marker`).
Folding is very useful when dealing with large files because you can scroll
through the file quickly and just unfold the function you wish to work on.
The `}}}` at the end of each function marks the end of the fold, and should
be on a separate line.
```c
/* {{{ Returns the absolute value of the number */
PHP_FUNCTION(abs)
{
...
}
/* }}} */
```
## New and experimental functions
To reduce the problems normally associated with the first public implementation
of a new set of functions, it has been suggested that the first implementation
include a file labeled `EXPERIMENTAL` in the function directory, and that the
functions follow the standard prefixing conventions during their initial
implementation.
The file labelled `EXPERIMENTAL` should include the following information:
* Any authoring information (known bugs, future directions of the module).
* Ongoing status notes which may not be appropriate for Git comments.
In general new features should go to PECL or experimental branches until there
are specific reasons for directly adding it to the core distribution.
## Aliases & legacy documentation
You may also have some deprecated aliases with close to duplicate names, for
example, `somedb_select_result` and `somedb_selectresult`. For documentation
purposes, these will only be documented by the most current name, with the
aliases listed in the documentation for the parent function. For ease of
reference, user-functions with completely different names, that alias to the
same function (such as `highlight_file` and `show_source`), will be separately
documented.
Backwards compatible functions and names should be maintained as long as the
code can be reasonably be kept as part of the codebase. See the `README` in the
PHP documentation repository for more information on documentation.