A summary of fourteen problems that cause headaches for PHP beginners

A summary of fourteen problems that cause headaches for PHP beginners_PHP Tutorial

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Release： 2016-07-21 15:49:09

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1. Variables cannot be transferred between pages
The automatic global variables of get, post, and session are turned off in the latest PHP version, 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 become familiar with the new writing method.
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. Win32 The session does not work properly
php.ini default session.save_path = /tmp
This is obviously the configuration under Linux. PHP cannot read and write the session file under win32, causing the session to be unusable
Put it away Just change it to an absolute path, for example, session.save_path = c:windowstemp
4. Display error message
When display_errors in php.ini = On and error_reporting = E_ALL, it will be displayed It is best to turn on all errors and prompts during debugging for error correction. If you use the previous PHP writing method, most of the error messages are about undefined variables. There will be a prompt when a variable is called before it is assigned a value. The solution is to detect or shield it.
For example, to display $foo, you can if(isset($foo)) echo $foo or echo @$foo
5. Mail() cannot send emails under Win32
In Linux The configured sendmail can be sent. Under win32, you need to call the smtp server to send emails. Modify the SMTP of php.ini = ip //ip is an smtp server without verification function (hard to find on the Internet), and php sends emails. The best solution 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
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 due to several reasons: 1. You PRING or ECHO before using HEADER. 2. There is something in front of your current file. Blank line 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. There is 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 in Installation on 2003 (I urge experts to advise on the ISAPI installation method)
PHP4’s php4isapi.dll seems to conflict with 2003, and can only be installed in CGI mode:
Step 1, first download to www.php.net An installation program
10. Sometimes the sql statement does not work and the database operation fails
The easiest debugging method is to echo the sql sentence and see if the value of the variable can be obtained.
11. The difference between include and require
There is not much difference between the two. If the file to be included does not exist, include will prompt a notice, and then continue to execute the following statement, and require will prompt a fatal error. And exit. According to my test, 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 that has been assigned a value is empty. If a variable is referenced in PHP without being assigned a value, it is allowed, but there will be a notice. If a variable is assigned a null value, $foo="" or $foo=0 or $foo=false, then empty($foo) returns true and isset($foo) also returns true, which means assigning a null value will not log out. a variable.
To unregister a variable, you can use unset($foo) or $foo=NULL.
13. The mysql query statement contains keywords
When PHP queries mysql, sometimes the mysql table name or column name contains keywords. There will be errors in the query at this time. 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. Method of uploading multiple files at one time through HTTP protocol
There are two ideas, which are two implementations of the same method. The specific procedures need to be designed by yourself:
1. Set up multiple file input boxes in the form and name them with arrays, as follows:

< ;input type=file name=usefile[]>

In this way, do the following tests on the server side
echo "

"; <br>print_r($_FILES); <br>echo "

";
2. Set multiple file input boxes in the form, but with different names, as follows:

Do the same test on the server side:
echo "

"; <br>print_r($_FILES); <br>echo "

";
Preface,
I installed: php-4.2.3-installer.exe, you can also find the latest one 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: Confirm;
Step 6: Select the PHP service extension and click Allow.