PHP 7.4无法加载php_mysqli.dll动态库，MySQL连接失败求助

Let’s work through this systematically—first, let’s rule out system/PHP configuration problems before we focus on Eclipse, since DLL loading failures almost always start there, not the IDE.

First: Verify the Problem Isn’t With PHP/System Configuration #

Start by testing outside of Eclipse to isolate the issue. Open Command Prompt and run these checks:

1. Confirm PHP Thread Safety (TS) vs Non-Thread Safety (NTS) Match #

PHP 7.4 on Windows comes in two flavors, and the php_mysqli.dll must match your PHP build:

• Run php -v in cmd. Look for "Thread Safe" in the output (e.g., PHP 7.4.33 (cli) (built: Aug 1 2023 11:50:48) ( ZTS Visual C++ 2017 x64 ) means Thread Safe).
• Check your C:\Program Files\php\ext directory: the DLL should be compiled for the same TS/NTS mode. If you downloaded the wrong PHP package, even the correct path won’t work—re-download the matching PHP version from the official site.

2. Install Required Visual C++ Redistributable #

PHP 7.4 depends on the Visual C++ Redistributable for Visual Studio 2017/2019 (VC15/VC16). Missing or outdated versions will break DLL loading:

• Download the x64 or x86 version matching your PHP architecture (check php -v for x64/x86) and install it. Restart your system after installation.

3. Fix Directory Permissions #

The C:\Program Files folder is protected by Windows UAC, which might block PHP from reading the DLL files:

• Copy your entire PHP directory to a non-system path like C:\php (avoid spaces in the path if possible, though PHP 7.4 handles them better than older versions).
• Update your php.ini to set extension_dir = "C:\php\ext", then run php -m again to see if mysqli loads.

4. Validate PHP.ini Configuration #

Double-check these settings in your active php.ini (run php --ini in cmd to confirm which php.ini PHP is using):

• Ensure extension_dir points directly to your ext folder (use absolute paths, no trailing slashes).
• Use the correct extension name: for PHP 7.4, it’s extension=mysqli (not extension=php_mysqli.dll—the .dll suffix is optional but often omitted in modern PHP configs).
• Make sure there’s no semicolon (;) before the extension=mysqli line (that comments it out).

If CLI Works But Eclipse Doesn’t: Check Eclipse Configuration #

If php -m shows mysqli is loaded correctly in the command line, then the issue is with Eclipse’s setup:

1. Confirm Eclipse is Using the Correct PHP Executable #

• Open Eclipse’s Window > Preferences > PHP > PHP Executables.
• Verify the path points to your working PHP php.exe (the one you tested in cmd).
• Check that the "PHP ini file" field points to the same php.ini you modified (not the default php.ini-development or php.ini-production unless you renamed one to php.ini).

2. Ensure Eclipse’s PHP Environment Matches CLI #

• Sometimes Eclipse uses a different PHP environment profile. Go to Run > Run Configurations, select your PHP script, and check the "PHP Executable" dropdown matches the working one from your cmd tests.

3. Clear Eclipse’s Cache #

IDE caches can hold outdated config data:

• Restart Eclipse with the -clean flag (open cmd, navigate to Eclipse’s installation folder, run eclipse.exe -clean).
• Refresh your project: right-click the project in Eclipse’s Project Explorer > Refresh.

Final Note #

If none of these steps work, try creating a simple test script (e.g., test.php with <?php phpinfo(); ?>) and run it via CLI (php test.php) to see if mysqli appears in the output. If it does, the problem is definitely Eclipse-specific—double-check all the IDE’s PHP settings again. If it still doesn’t load, you may need to re-download a fresh copy of PHP 7.4 (make sure to pick the correct TS/NTS and architecture) and start with a clean php.ini configuration.

内容的提问来源于stack exchange，提问作者StevieJ123