Summary of writing PHP code_PHP tutorial

1- Write modular code

Good PHP code should be modular code. PHP's object-oriented programming capabilities are particularly powerful tools for breaking your application into functions or methods. You should separate as much as possible the front-end HTML/CSS/JavaScript code from the server-side of your application. You can also follow the MVC (Model-View-Controller) pattern on any PHP framework.

2- Code writing standards

Good PHP code should have a complete set of code writing specifications. Achieving programming standards through naming variables and functions, unified methods for accessing the database and handling errors, and the same code indentation method can make your code more readable.

3- Write portable code

Good PHP code should be portable. You can use PHP's existing features like magic quotes and short tags. Try to understand your needs and then write code to make it self-contained and portable by adapting PHP features.

4- Write secure code

Good PHP code should be safe. PHP5 provides excellent performance and flexibility. But the security issue lies entirely with the developers. For a professional PHP developer, it is crucial to have a deep understanding of major security vulnerabilities, such as: cross-site scripting (XSS), cross-site request forgery (CSRF), code injection vulnerabilities, and character encoding vulnerabilities. By using PHP's special features and functions, such as: mysql_real_escape_string, etc., you can write safe code.

5- Code Comments

Code comments are an important part of the code. Through code comments, you can know what the variable or function does, which will be very useful in future code maintenance.

6- Avoid short tags

Replace all short tags with full PHP tags.

7- Use single quotes instead of double quotes

Strings always use single quotes instead of double quotes to avoid performance degradation caused by PHP searching for variables within the string. It's faster to enclose the string in single quotes instead of double quotes. Because PHP will search for variables in a string surrounded by double quotes, single quotes will not

8- Escaped string output

It is a good practice to pass ENT_QUOTES as argument to the htmlspecialchars function to ensure that single quotes (') are also converted to HTML entities.

9- Use comma separated string output

Outputting a string separated by commas (,) through the echo statement has better performance than using the string concatenation operator (.).

10- Check the passed value before output

Check the passed value $_GET['query'] before outputting. Using the isset or empty function, you can check whether a variable is null.

11- Others

• If you can define a class method as static, try to define it as static, and its speed will be increased by nearly 4 times.
• $row['id'] is 7 times faster than $row[id].
• echo is faster than print, and uses multiple parameters of echo (annotation: refers to using commas instead of periods) instead of string concatenation, such as echo $str1, $str2.
• Determine the maximum number of loops before executing the for loop. Do not calculate the maximum value every loop. It is best to use foreach instead.
• Unregister unused variables, especially large arrays, to free up memory.
• Try to avoid using __get, __set, __autoload.
• require_once() is expensive.
• Try to use absolute paths when including files, because it avoids the speed of PHP searching for files in include_path, and the time required to parse the operating system path will be less.
• If you want to know the time when the script starts executing (annotation: the server receives the client request), using $_SERVER['REQUEST_TIME'] is better than time().
• Function replaces regular expression to accomplish the same function.
• The str_replace function is faster than the preg_replace function, but the strtr function is four times more efficient than the str_replace function.
• If a string replacement function accepts arrays or characters as parameters, and the parameter length is not too long, then you can consider writing an additional replacement code so that each parameter passed is a character, instead of just writing one line of code to accept it Arrays as parameters for queries and replaces.
• It is better to use a selective branch statement (Translation: switch case) than to use multiple if, else if statements.
• Using @ to block error messages is very inefficient, extremely inefficient.
• Open apache's mod_deflate module to improve web browsing speed.
• The database connection should be closed when finished using it, and do not use long connections.
• Error messages are expensive.
• Incrementing local variables in methods is the fastest. Almost as fast as calling local variables in a function.
• Incrementing a global variable is 2 times slower than incrementing a local variable.
• Incrementing an object property (eg: $this->prop++) is 3 times slower than incrementing a local variable.
• Incrementing an undefined local variable is 9 to 10 times slower than incrementing a predefined local variable.
• Just defining a local variable without calling it in a function will also slow things down (to the same extent as incrementing a local variable). PHP will probably check to see if a global variable exists.
• Method calls appear to be independent of the number of methods defined in the class, as I added 10 methods (both before and after testing the method) and there was no change in performance.
• Methods in derived classes run faster than the same methods defined in base classes.
• Calling an empty function with one parameter takes the same time as performing 7 to 8 local variable increment operations. A similar method call takes close to 15 local variable increment operations.
• Apache parses a PHP script 2 to 10 times slower than parsing a static HTML page. Try to use more static HTML pages and less scripts.
• Unless the script can be cached, it will be recompiled each time it is called. Introducing a PHP caching mechanism can usually improve performance by 25% to 100% to eliminate compilation overhead.
• Cache as much as possible, you can use memcached. Memcached is a high-performance memory object caching system that can be used to accelerate dynamic web applications and reduce database load. Caching of OP codes is useful so that scripts do not have to be recompiled for each request.
• When operating a string and need to check whether its length meets certain requirements, you will naturally use the strlen() function. This function executes fairly quickly because it doesn't do any calculations and just returns the known string length stored in the zval structure (C's built-in data structure used to store PHP variables). However, since strlen() is a function, it will be somewhat slow, because the function call will go through many steps, such as lowercase letters (Annotation: refers to the lowercase function name, PHP does not distinguish between uppercase and lowercase function names), hash search, Will be executed together with the called function. In some cases, you can use the isset() trick to speed up the execution of your code.

  （举例如下）  if (strlen($foo) < 5) { echo 'Foo is too short'; } 

• （与下面的技巧做比较）  if (!isset($foo[5])) { echo 'Foo is too short'; }    

  Calling isset() happens to be faster than strlen(), because unlike the latter, isset(), as a language construct, means that its execution does not require function lookup and letter lowercase. That is, you actually don't spend much overhead in the top-level code checking the string length.

• When executing the increment or decrement of variable $i, $i++ will be slower than ++$i. This difference is specific to PHP and does not apply to other languages, so please don't modify your C or Java code and expect it to be instantly faster, it won't work. ++$i is faster because it only requires 3 instructions (opcodes), while $i++ requires 4 instructions. Postincrement actually creates a temporary variable that is subsequently incremented. Prefix increment increases directly on the original value. This is a form of optimization, as done by Zend's PHP optimizer. It's a good idea to keep this optimization in mind because not all command optimizers perform the same optimizations, and there are a large number of Internet Service Providers (ISPs) and servers that do not have command optimizers installed.
• Everything does not have to be object-oriented (OOP). Object-oriented is often very expensive, and each method and object call consumes a lot of memory.
• Not all data structures need to be implemented with classes, arrays are also useful.
• Don’t break down the methods too much. Think carefully about which code you really intend to reuse?
• You can always break your code into methods when you need to.
• Try to use a large number of PHP built-in functions.
• If there are a lot of time-consuming functions in your code, you can consider implementing them as C extensions.
• Profile your code. The checker will tell you which parts of the code take how much time. The Xdebug debugger includes inspection routines that evaluate the overall integrity of your code and reveal bottlenecks in your code.
• mod_zip can be used as an Apache module to instantly compress your data and reduce data transfer volume by 80%.
• When file_get_contents can be used instead of file, fopen, feof, fgets and other series of methods, try to use file_get_contents because it is much more efficient! But please pay attention to the PHP version problem of file_get_contents when opening a URL file;
• Carry out as few file operations as possible, although PHP’s file operations are not inefficient;
• Optimize the Select SQL statement and perform as few Insert and Update operations as possible (I was criticized for updating);
• Use PHP internal functions as much as possible (but in order to find a function that does not exist in PHP, I wasted time that could have been written a custom function, a matter of experience!);
• Do not declare variables inside the loop, especially large variables: objects (this seems to be not just a problem in PHP, right?);
• Try not to nest assignments in loops for multi-dimensional arrays;
• Do not use regular expressions when you can use PHP’s internal string manipulation functions;
• foreach is more efficient, try to use foreach instead of while and for loop;
• "Replace i=i+1 with i+=1. It conforms to the habits of c/c++ and is more efficient";
• Global variables should be unset()ed after use;

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