1. Notices
These are relatively small and not serious errors, such as accessing an undefined variable. Usually, such errors are not prompted to the user, but sometimes these errors will affect the results of the operation.
2. Warnings
This is a slightly more serious error, such as trying to include() a file that does not exist. Such an error message will be prompted to the user, but will not cause the program to terminate.
3. Fatal errors
These are serious errors. For example, if you want to initialize an object of a class that does not exist at all, or call a function that does not exist, these errors will cause the program to stop running. PHP These errors will also be displayed to the user.
Different error types include:
E_ERROR: Usually displayed, it can also interrupt program execution.
E_WARNING: Usually displayed, but will not interrupt program execution.
E_NOTICE: A code error that occurs when the script is running normally.
E_PARSE: Syntax parsing error.
E_CORE_ERROR: Fatal error that occurred during PHP startup.
E_CORE_WARNING: Report non-fatal errors that occur when PHP starts.
E_COMPILE_ERROR: Fatal error that occurs during compilation, indicating errors in the script.
E_USER_ERROR: User-generated error message.
E_USER_WARNING: Warning message generated by the user.
E_USER_NOTICE: Attention message caused by user.
E_STRICT: Encoding standardization warning, error that occurs at runtime.
E_RECOVERABLE_ERROR: A near-fatal runtime error. If not caught, it will be treated as E_ERROR.
E_ALL: Catch all errors and warnings.
The method to shield PHP error prompts is as follows
Method 1: Add @ before the function that may cause errors, and then or die("")
For example:
@mysql_connect(...) or die("Database Connect Error")
Method 2: Edit php.ini, search for "display_errors=", and change the value after "=" to "off.
Method 3: Add error_reporting(0) in front of the php script to block all errors. Tip.
Among them, error_reporting configures the level of error information reporting.
Syntax: int error_reporting(int [level]);
Return value: integer
Function type: PHP system function

PHPsessionscanstorestrings,numbers,arrays,andobjects.1.Strings:textdatalikeusernames.2.Numbers:integersorfloatsforcounters.3.Arrays:listslikeshoppingcarts.4.Objects:complexstructuresthatareserialized.

TostartaPHPsession,usesession_start()atthescript'sbeginning.1)Placeitbeforeanyoutputtosetthesessioncookie.2)Usesessionsforuserdatalikeloginstatusorshoppingcarts.3)RegeneratesessionIDstopreventfixationattacks.4)Considerusingadatabaseforsessionstoragei

Session regeneration refers to generating a new session ID and invalidating the old ID when the user performs sensitive operations in case of session fixed attacks. The implementation steps include: 1. Detect sensitive operations, 2. Generate new session ID, 3. Destroy old session ID, 4. Update user-side session information.

PHP sessions have a significant impact on application performance. Optimization methods include: 1. Use a database to store session data to improve response speed; 2. Reduce the use of session data and only store necessary information; 3. Use a non-blocking session processor to improve concurrency capabilities; 4. Adjust the session expiration time to balance user experience and server burden; 5. Use persistent sessions to reduce the number of data read and write times.

PHPsessionsareserver-side,whilecookiesareclient-side.1)Sessionsstoredataontheserver,aremoresecure,andhandlelargerdata.2)Cookiesstoredataontheclient,arelesssecure,andlimitedinsize.Usesessionsforsensitivedataandcookiesfornon-sensitive,client-sidedata.

PHPidentifiesauser'ssessionusingsessioncookiesandsessionIDs.1)Whensession_start()iscalled,PHPgeneratesauniquesessionIDstoredinacookienamedPHPSESSIDontheuser'sbrowser.2)ThisIDallowsPHPtoretrievesessiondatafromtheserver.

The security of PHP sessions can be achieved through the following measures: 1. Use session_regenerate_id() to regenerate the session ID when the user logs in or is an important operation. 2. Encrypt the transmission session ID through the HTTPS protocol. 3. Use session_save_path() to specify the secure directory to store session data and set permissions correctly.

PHPsessionfilesarestoredinthedirectoryspecifiedbysession.save_path,typically/tmponUnix-likesystemsorC:\Windows\TemponWindows.Tocustomizethis:1)Usesession_save_path()tosetacustomdirectory,ensuringit'swritable;2)Verifythecustomdirectoryexistsandiswrita


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