PHP writing large website problem set_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.
Part 1, 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.

Copy code The code is as follows:

　/*
　* The three faces of Π
*/

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

But many programmers just want to display some variable values ​​and functions The return value uses this function. Because Printf() formats the data before displaying it, it 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:

Copy code The code is as follows:

Boolean, resource, integer , double, string, array and object

3. Use of temporary variables
The 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:

Copy code The code is as follows:

　$tmp = date ("F d, h:i a"); /* ie January 3, 2:30 pm */
　print $tmp;
?>

should be changed to:

Copy code The code is as follows:

　print date ("F d, h:i a");
?>

Another example:

Copy code The code is as follows:

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

?>

It is not very readable and can be changed to:

Copy code The code is as follows:

// 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. Client and server Separation of client-side code
The client-side and server-side code in the PHP program are actually HTML code and PHP language code. Many people mix HTML and PHP statements in one file, making the file very large. This style It is very detrimental to the maintenance and redevelopment of the program and is not suitable for the development of large sites. There are generally two methods to separate HTML and PHP statements:
1. Write a dedicated API, for example:

index.php The Client side

Copy code The code is as follows:

site.lib The server side code

复制代码 代码如下:

$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：

复制代码 代码如下:

%%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。这种方法的缺点是执行效率不高，因为要解释模板文件。同时实现起来也比较复杂。

注： www.thewebmasters.net的 FastTemplate class可方便的实现以上功能，或者使用 Smarty 模板引擎

五、不要用过时的函数
作为一种自由软件，PHP发展很快，其中的很多函数都已过时，例如：

复制代码 代码如下:

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

虽然还能用但效率肯定不高，而且可能在以后的版本中会禁用，导致程序不能运行。因此要经常对照最新PHP手册检查那些函数已过时及时修正。

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