Summary of the most confusing questions for PHP beginners

Summary of the most confusing questions for PHP beginners_PHP Tutorial

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Release： 2016-07-21 15:40:07

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[1] Variables get, post, and session cannot be transferred between pages. In the latest PHP version, automatic global variables are turned off, so to get the submitted variables from the previous page, use $_GET['foo'], $_POST. ['foo'],$_SESSION['foo'] to get
Of course, you can also modify the automatic global variables to be on (php.ini is changed to register_globals = On); considering compatibility, it is better to force yourself to be familiar with the new way of writing Better.
[2] Using the get method to pass Chinese parameters to apache2 under Win32 will cause an error
test.php?a=Hello&b=Hello
Passing parameters will cause an internal error
Solution: "test.php?a=".urlencode(Hello)."&b=".urlencode(Hello)
.............

【3 】The session under win32 does not work properly
php.ini default session.save_path = /tmp
This is obviously the configuration under linux. PHP under win32 cannot read and write the session file, causing the session to be unusable
Put it away Just change it to an absolute path, for example, session.save_path = c:windows emp
【4】Display error message
When display_errors in php.ini = On and error_reporting = E_ALL, all errors and Tip, it is best to turn it on during debugging for error correction. If you use the previous PHP writing method, the error message is mostly about undefined variables. There will be a prompt when a variable is called before being assigned. The solution is to detect or block
. For example, if $foo is displayed, you can if(isset($foo)) echo $foo or echo @$foo
【5】mail( under Win32 ) cannot send emails
The configured sendmail under Linux can be sent, but under win32 you need to call the smtp server to send emails
Modify the SMTP of php.ini = ip //ip is smtp without verification function Server (difficult to find online)
The best solution for PHP to send emails is to use socket to send directly to the other party's email server without forwarding the server
[6] If the password is not set for the initial installation of mysql, you should use it
update mysql.user set password="yourpassword" where user="root"
Change password
【7】header already sent
This error usually occurs when you use HEADER. It may be several Reasons: 1. You PRING or ECHO before using HEADER 2. There is a blank line in front of your current file 3. You may have INCLUDEd a file and there is a blank line at the end of the file or this error will occur in the output. !
【8】No change after changing php.ini
Restart the web server, such as IIS, Apache, etc., and then the latest settings will be applied
【9】php is installed on 2003 (ISAPI installation Please advise experts on the method)
PHP4’s php4isapi.dll seems to conflict with 2003, and can only be installed in CGI mode.
Step 1, first download an installation program from www.php.net, I installed: php -4.2.3-installer.exe, you can also find the latest version. Make sure your IIS6.0 is started and accessible before installing php-4.2.3-installer.exe. After installation, go to the default website-->Application Configuration
Step 2: Click web service extension-->New web service extension.
Step 3: Extension-->php, and then add
Step 4: Find the path to php.exe and add it.
Step 5: Just confirm!
Step 6: Select the php service extension and click Allow.
【10】
Sometimes the sql statement does not work and the database operation fails
The easiest way to debug is to echo the sql sentence and see if the value of the variable can be obtained
【11】include The difference between require and require
There is not much difference between the two. If the file to be included does not exist, include prompts notice, and then continues to execute the following statement. require prompts a fatal error and exits
According to my testing, under the win32 platform They are included first and then executed, so it is best not to have include or require statements in the included files, which will cause directory confusion. Maybe the situation is different in *nux, I haven’t tested it yet
If you don’t want a file to be included multiple times, you can use include_once or require_once## to read and write document data

Copy code The code is as follows:

 
function r($file_name) { 
$filenum=@fopen($file_name,"r"); 
@flock($filenum ,LOCK_SH); 
$file_data=@fread($filenum,filesize($file_name)); 
@fclose($filenum); 
return $file_data; 
} 
function w( $file_name,$data,$method="w"){ 
$filenum=@fopen($file_name,$method); 
flock($filenum,LOCK_EX); 
$file_data=fwrite($ filenum,$data); 
fclose($filenum); 
return $file_data; 
} 

【12】The difference between isset() and empty()
Both are used to test variables
But isset() tests whether a variable has been assigned a value, while empty() tests whether a variable has been assigned a value. Whether the variable is empty
If a variable is not assigned a value, it is allowed to be referenced in PHP, but there will be a notice prompt
If a variable is assigned a null value, $foo="" or $foo=0 Or $foo=false, then empty($foo) returns true and isset($foo) also returns true, which means assigning a null value will not unregister a variable.
To unregister a variable, you can use unset($foo) or $foo=NULL
[13] The mysql query statement contains keywords
When php queries mysql, sometimes the mysql table name or column name There will be keywords
. At this time, the query will have errors. For example, if the table name is order, an error will occur during query
The simple way is to add `[above the tab key] to the table name or column name in the SQL statement to distinguish it
For example, select * from `order`
【 14] The method of uploading multiple files at one time through HTTP protocol
has two ideas, which are two implementations of the same method. The specific program needs to be designed by yourself
1. Set up multiple file input boxes in the form and name them with arrays, as follows:

Copy code The code is as follows:

In this way, do the following test on the server side

Copy code The code is as follows:

echo "