40个技巧优化你的PHP代码
英文版权归Reinhold Weber所有，中译文作者yangyang（aka davidkoree）。双语版可用于非商业传播，但须注明英文版作者、版权信息，以及中译文作者。


1. If a method can be static, declare it static. Speed improvement is by a factor of  如果一个方法可静态化，就对它做静态声明。速率可提升至4倍。

2. echo is faster than print. echo 比 print 快。

3. Use echo’s multiple parameters instead of string concatenation. 使用echo的多   重参数（译注：指用逗号而不是句点）代替字符串连接。

4. Set the maxvalue for your for-loops before and not in the loop. 在执行for循环之前确定最大循环数，不要每循环一次都计算最大值。

5. Unset your variables to free memory, especially large arrays. 注销那些不用的变量尤其是大数组，以便释放内存。

6. Avoid magic like __get, __set, __autoload 尽量避免使用__get，__set，__autoload。

7. require_once() is expensive require_once()代价昂贵。

8. Use full paths in includes and requires, less time spent on resolving the OS paths. 在包含文件时使用完整路径，解析操作系统路径所需的时间会更少。

9. If you need to find out the time when the script started executing, $_SERVER[’REQUEST_TIME’] is preferred to time() 如果你想知道脚本开始执行（译注：即服务器端收到客户端请求）的时刻，使用$_SERVER[‘REQUEST_TIME’]要好于time()。

10. See if you can use strncasecmp, strpbrk and stripos instead of regex. 检查是否能用strncasecmp，strpbrk，stripos函数代替正则表达式完成相同功能。

11. str_replace is faster than preg_replace, but strtr is faster than str_replace by a factor of 4. str_replace函数比preg_replace函数快，但strtr函数的效率是str_replace函数的四倍。

12. If the function, such as string replacement function, accepts both arrays and single characters as arguments, and if your argument list is not too long, consider writing a few redundant replacement statements, passing one character at a time, instead of one line of code that accepts arrays as search and replace arguments. 如果一个字符串替换函数，可接受数组或字符作为参数，并且参数长度不太长，那么可以考虑额外写一段替换代码，使得每次传递参数是一个字符，而不是只写一行 代码接受数组作为查询和替换的参数。

13. It’s better to use select statements than multi if, else if, statements. 使用选择分支语句（译注：即switch case）好于使用多个if，else if语句。

14. Error suppression with @ is very slow. 用@屏蔽错误消息的做法非常低效。

15. Turn on apache’s mod_deflate 打开apache的mod_deflate模块。

16. Close your database connections when you’re done with them. 数据库连接当使用完毕时应关掉。

17. $row[’id’] is 7 times faster than $row[id]. $row[‘id’]的效率是$row[id]的7倍。

18. Error messages are expensive. 错误消息代价昂贵。

19. Do not use functions inside of for loop, such as for ($x=0; $x < count($array); $x) The count() function gets called each time. 尽量不要在for循环中使用函数，比如for ($x=0; $x < count($array); $x)每循环一次都会调用count()函数。

20. Incrementing a local variable in a method is the fastest. Nearly the same as calling a local variable in a function. 在方法中递增局部变量，速度是最快的。几乎与在函数中调用局部变量的速度相当。

21. Incrementing a global variable is 2 times slow than a local var. 递增一个全局变量要比递增一个局部变量慢2倍。

22. Incrementing an object property (eg. $this->prop++) is 3 times slower than a local variable. 递增一个对象属性（如：$this->prop++）要比递增一个局部变量慢3倍。

23. Incrementing an undefined local variable is 9-10 times slower than a pre-initialized one. 递增一个未预定义的局部变量要比递增一个预定义的局部变量慢9至10倍。

24. Just declaring a global variable without using it in a function also slows things down (by about the same amount as incrementing a local var). PHP probably does a check to see if the global exists. 仅定义一个局部变量而没在函数中调用它，同样会减慢速度（其程度相当于递增一个局部变量）。PHP大概会检查看是否存在全局变量。

25. Method invocation appears to be independent of the number of methods defined in the class because I added 10 more methods to the test class (before and after the test method) with no change in performance. 方法调用看来与类中定义的方法的数量无关，因为我（在测试方法之前和之后都）添加了10个方法，但性能上没有变化。

26. Methods in derived classes run faster than ones defined in the base class. 派生类中的方法运行起来要快于在基类中定义的同样的方法。

27. A function call with one parameter and an empty function body takes about the same time as doing 7-8 $localvar++ operations. A similar method call is of course about 15