Collection of problems in writing large websites in PHP_PHP tutorial

PHP has been rapidly promoted for its ease of use, but ease of use does not mean that you can use it well. In fact, many programmers use it to easily build WEB application systems, but how many people have carefully considered them? Whether the code is easy to maintain, robust enough, efficient enough, and secure enough, these become critical factors when PHP is used to build large websites. Let's start with the more minor issues and move on to some fatal mistakes. It is divided into three parts.
The first part, minor errors

1. Printf(),
This function is mainly used to format and display data. Use it only when you want to change the display format of certain data.
For example, display the value of PI (3.1415926) with different precisions.
/*
* The three faces of Π
*/

printf ("Pi is: %.2fn
n", M_PI);
printf ("Pi is also: %.3fn
n", M_PI);
printf ("Pi is also: %.4fn
n", M_PI);
?>

But many programmers only use this function to display some variable values ​​and function return values. Because Printf() must format the data before displaying the data, the speed is slow. Therefore, print and echo are only used when displaying the data to increase the speed.

2. Semantic check
PHP is a weakly typed language, which means that there is no need to define a variable before using it. This brings great convenience and flexibility to programming, but you must know it yourself What type should the variable be? Because the variable actually corresponds to a certain type at runtime (various types can be freely converted to each other), and variables without types do not exist. It is possible that PHP cannot detect your semantic errors, but due to changes in variable types, some potential problems may occur. Another issue worth noting is the scope of variables, which may also cause some potential problems.
There are the following basic variables in PHP:
Boolean, resource, integer, double, string, array and object.

3. Use of temporary variables
Abuse of temporary variables will lead to a reduction in program operating efficiency. When to use temporary variables can be based on the following two considerations:
1. Whether the variable is used at least twice.
2. Whether the use of this variable will significantly improve the readability of the program.
If none of the above is satisfied, the use of this variable is omitted. For example:
$tmp = date ("F d, h:i a"); /* ie January 3, 2:30 pm */
print $tmp;
?>
should be changed to:
print date ("F d, h:i a");
?>

Another example:

// string reverse_characters(string str)
// Reverse all of the characters in a string.
function reverse_characters ($str)
{
return implode ("", array_reverse (preg_split("//", $str)));
}

?>
is not very readable and can be changed to:

// string reverse_characters(string str)
// Reverse all of the characters in a string.
function reverse_characters ($str)
{
$characters = preg_split ("//", $str);
$characters = array_reverse ($characters);

return implode ("", $characters);
}

?>

4. Separation of client-side and server-side code
The client-side and server-side codes in PHP programs are actually HTML code and PHP language code. Many people regard HTML and server-side code as PHP statements are mixed in one file, making the file very large. This style is very detrimental to program maintenance and redevelopment, and is not suitable for the development of large sites.一般有两种方法把HTML和PHP语句分开： 
  1、编写专用API，例如： 

  index.php ？ The Client side 
   
   
   
   
   
   
  

  

 
   
   
   
   
   
   
   
   
   
   
   
   

   
  site.lib ？ The server side code 

   
  
  $dbh = mysql_connect ("localhost", "sh", "pass") 
  or die (sprintf ("Cannot connect to MySQL [%s]: %s", 
  mysql_errno (), mysql_error ())); 
  @mysql_select_db ("MainSite") 
  or die (sprintf ("Cannot select database [%s]: %s", 
  mysql_errno (), mysql_error ())); 

  $sth = @mysql_query ("SELECT * FROM site", $dbh) 
  or die (sprintf ("Cannot execute query [%s]: %s", 
  mysql_errno (), mysql_error ())); 

  $site_info = mysql_fetch_object ($sth); 

  function print_header () 
  { 
  　global $site_info; 
  　print $site_info->header; 
  } 

  function print_body () 
  { 
  　global $site_info; 
  　print nl2br ($site_info->body); 
  } 

  function print_links () 
  { 
  　global $site_info; 

  　$links = explode ("n", $site_info->links); 
  　$names = explode ("n", $site_info->link_names); 

  for ($i = 0; $i < count ($links); $i++) 
  { 
  　print "ttt 
  　$names[$i] 
  　n
n"; 
  } 
  } 
  ?> 

  这种方法使得程序看起来比较简洁，而且执行速度也较快。 

  2、使用模板的方法 
  这种方法使得程序看起来更简洁，同样实现上面的功能，可用以下代码： 
   
   
   
   
   
  

%%PAGE_TITLE%%

 
   
   
  %%PAGE_LINKS%% 
  %%PAGE_CONTENT%% 
   
   
   
   

  　　用占位符代替要动态生成的内容，然后用一解析程序分析该模板文件，把占位符用际的内容替换。种方法使得即使不会使用PHP的页面制作人员也能修改模板文件。The disadvantage of this method is that the execution efficiency is not high because the template file needs to be interpreted. At the same time, it is also more complicated to implement.

Note: www.thewebmasters.net’s FastTemplate class can easily implement the above functions.

5. Don’t use outdated functions
As a free software, PHP is developing rapidly, and many of its functions are outdated, such as:

while (1):
print "5";
if ($idx++ == 5):
break;
endif;
endwhile;

Although it can still be used, it is definitely not efficient, and It may be disabled in future versions, causing the program to not run. Therefore, you should always check the latest PHP manual to check which functions are outdated and correct them in time.

http://www.bkjia.com/PHPjc/317863.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/317863.htmlTechArticlePHP has been rapidly promoted for its ease of use, but ease of use does not mean that you can use it well. In fact, Many programmers use it to easily build WEB application systems, but how many people carefully consider...