InPHP,variablesarepassedbyvaluebydefault,meaningfunctionsorassignmentsreceiveacopyofthedata,whilepassingbyreferenceallowsmodificationstoaffecttheoriginalvariable.1.Whenpassingbyvalue,changestothecopydonotimpacttheoriginal,asshownwhenassigning$b=$aorp

To safely handle PHP file uploads, you need to verify the source and type, control the file name and path, set server restrictions, and process media files twice. 1. Verify the upload source to prevent CSRF through token and detect the real MIME type through finfo_file using whitelist control; 2. Rename the file to a random string and determine the extension to store it in a non-Web directory according to the detection type; 3. PHP configuration limits the upload size and temporary directory Nginx/Apache prohibits access to the upload directory; 4. The GD library resaves the pictures to clear potential malicious data.

If the second monitor is not recognized by Windows, first check whether the cable and interface are normal, try to replace the HDMI, DP or VGA cable, confirm the plug-in video output port, and test different interfaces to eliminate compatibility issues; then verify the monitor power and input source settings, and connect the monitor separately to test whether it can be recognized; then enter the Windows display settings and click the "Detection" button, or use Win P to switch the display mode, and update the graphics card driver at the same time; finally check the graphics card specifications to confirm whether it supports multi-screen output to avoid exceeding its maximum output capability.

The most direct way to find the last occurrence of a substring in PHP is to use the strrpos() function. 1. Use strrpos() function to directly obtain the index of the last occurrence of the substring in the main string. If it is not found, it returns false. The syntax is strrpos($haystack,$needle,$offset=0). 2. If you need to ignore case, you can use the strripos() function to implement case-insensitive search. 3. For multi-byte characters such as Chinese, the mb_strrpos() function in the mbstring extension should be used to ensure that the character position is returned instead of the byte position. 4. Note that strrpos() returns f

When you encounter the "DefaultGatewayisNotAvailable" prompt, it means that the computer cannot connect to the router or does not obtain the network address correctly. 1. First, restart the router and computer, wait for the router to fully start before trying to connect; 2. Check whether the IP address is set to automatically obtain, enter the network attribute to ensure that "Automatically obtain IP address" and "Automatically obtain DNS server address" are selected; 3. Run ipconfig/release and ipconfig/renew through the command prompt to release and re-acquire the IP address, and execute the netsh command to reset the network components if necessary; 4. Check the wireless network card driver, update or reinstall the driver to ensure that it works normally.

When encountering the "SYSTEM_SERVICE_EXCEPTION" blue screen error, you do not need to reinstall the system or replace the hardware immediately. You can follow the following steps to check: 1. Update or roll back hardware drivers such as graphics cards, especially recently updated drivers; 2. Uninstall third-party antivirus software or system tools, and use WindowsDefender or well-known brand products to replace them; 3. Run sfc/scannow and DISM commands as administrator to repair system files; 4. Check memory problems, restore the default frequency and re-plug and unplug the memory stick, and use Windows memory diagnostic tools to detect. In most cases, the driver and software problems can be solved first.

When the boot prompt is "Windows could not start because of the following fileismissing" 1. You can run bootrec/fixmb, bootrec/fixboot, bootrec/rebuildbcd through the Windows installation media; 2. Check the hard disk connection or use CrystalDiskInfo to detect the health status of the hard disk; 3. If there is a dual system, you can use the bootrec command to rebuild the boot or manually add the boot items; 4. Use PE environment to kill viruses and combine DISM and SFC tools to repair the system files, and the system can be restored in most cases.

The reason why header('Location:...') in AJAX request is invalid is that the browser will not automatically perform page redirects. Because in the AJAX request, the 302 status code and Location header information returned by the server will be processed as response data, rather than triggering the jump behavior. Solutions are: 1. Return JSON data in PHP and include a jump URL; 2. Check the redirect field in the front-end AJAX callback and jump manually with window.location.href; 3. Ensure that the PHP output is only JSON to avoid parsing failure; 4. To deal with cross-domain problems, you need to set appropriate CORS headers; 5. To prevent cache interference, you can add a timestamp or set cache:f