PHP experts share useful information: 50 details you must read! [PHP training tutorial]

Brothers share useful information for PHP masters: 50 details you must read

1. Use single quotes instead of double quotes to include strings, which will be faster. Because PHP will search for variables in strings surrounded by double quotes, single quotes will not. Note: only echo can do this, it is a "function" that can take multiple strings as parameters (Annotation: PHP Manual It is said that echo is a language structure, not a real function, so the function is enclosed in double quotes).

　 2. If you can define a class method as static, try to define it as static, and its speed will increase by nearly 4 times.

　 3. The speed of $row[‘id’] is 7 times that of $row[id].

　　4. 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.

　5. 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.

　6. Unregister unused variables, especially large arrays, to free up memory.

　7. Try to avoid using __get, __set, __autoload.

　8. require_once() is expensive.

　9. 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.

　10. If you want to know the time when the script starts executing (annotation: the server receives the client request), it is better to use $_SERVER['REQUEST_TIME'] than time()

　11. Functions replace regular expressions to accomplish the same thing Function.

　12. 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.

　13. If a string replacement function can accept 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. Accepts arrays as parameters for query and replace.

　14. It is better to use a selective branch statement (translation annotation: switch case) than to use multiple if, else if statements.

　15. Using @ to block error messages is very inefficient, extremely inefficient.

　16. Opening the mod_deflate module of apache can improve the browsing speed of web pages.

　17. The database connection should be closed when finished using it. Do not use long connections.

　18. Error messages are expensive.

　19. Increasing local variables in methods is the fastest. Almost as fast as calling local variables in a function.

　20. Incrementing a global variable is 2 times slower than incrementing a local variable.

　21. Incrementing an object property (such as: $this->prop++) is 3 times slower than incrementing a local variable.

　22. Incrementing an undefined local variable is 9 to 10 times slower than incrementing a predefined local variable.

　 23. Just defining a local variable without calling it in a function will also slow down the speed (to the same extent as incrementing a local variable). PHP will probably check to see if a global variable exists.

　24. Method calls appear to be independent of the number of methods defined in the class, because I added 10 methods (both before and after testing the method), but there was no change in performance.

　 25. Methods in derived classes run faster than the same methods defined in base classes.

　 26. 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 increments.

　 27. The time for Apache to parse a PHP script is 2 to 10 times slower than parsing a static HTML page. Try to use more static HTML pages and less scripts.

　28. Unless the script can be cached, it will be recompiled every time it is called. Introducing a PHP caching mechanism can usually improve performance by 25% to 100% to eliminate compilation overhead.

　29. Try to 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.

　　30. 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.

　(Examples are as follows)

if (strlen($foo)
　(Compare with the following technique)

　 if (!isset($foo{5})) { echo “Foo is too short”$$ }

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

　31. When performing increment or decrement of variable $i, $i++ will be slower than ++$i. This difference is unique to PHP and does not apply to other languages. Please don't modify your C or Java code and expect it to be faster immediately, it won't work. ++$i is faster because it only requires 3 instructions (opcodes), $i++ requires 4 instructions for post-increment. A temporary variable is actually created, which is then incremented by the original value. This is a kind of optimization, just like what Zend's PHP optimizer does. A good idea, because not all command optimizers do the same optimization, and there are a large number of Internet Service Providers (ISPs) and servers that do not have command optimizers installed.

　　32. Not necessarily object-oriented (OOP). ), object-oriented is often very expensive, and each method and object call consumes a lot of memory.

　33. It is not necessary to use classes to implement all data structures. Arrays are also very useful. 34. Don’t subdivide methods too much. More, think carefully about which code you really plan to reuse?

　　35. When you need, you can always break the code into methods

　　36. Try to use a lot of PHP built-in functions

　37. There are a lot of time-consuming functions in the code, you can consider using C extensions to implement them.

　　38. Profile your code. The checker will tell you which parts of the code take how much time to debug. The compiler includes a verification program, and the overall evaluation verification can show the bottlenecks of the code.

　39. mod_zip can be used as an Apache module to instantly compress your data and reduce the data transfer volume by 80%. 40. In 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 pay attention to the PHP version problem of file_get_contents when opening a URL file;

　　41. Try to Perform less file operations, although PHP's file operation efficiency is not low;

　42. Optimize the Select SQL statement and perform as few Insert and Update operations as possible (I have been criticized for updates) ;

　 43. 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!);

　 44. Loop Do not declare variables internally, especially large variables: objects (this seems to be not just a problem in PHP, right?);

　　45. Try not to loop nested assignments in multi-dimensional arrays;

　46. You can use PHP internal strings When operating functions, do not use regular expressions;

　47. foreach is more efficient, try to use foreach instead of while and for loops;

　48. Use single quotes instead of double quotes to quote strings;

　49. Use " i+=1 instead of i=i+1. It conforms to the habits of c/c++ and is very efficient."

50. For global variables, you should unset() them after use