Fatal error: Call to undefined function sqlsrv_connect()

This helped me get to my answer. There are two php.ini files located, in my case, for wamp. One is under the php folder and the other one is in the C:\wamp\bin\apache\Apachex.x.x\bin folder. When connecting to SQL through sqlsrv_connect function, we are referring to the php.ini file in the apache folder. Add the following (as per your version) to this file:

extension=c:/wamp/bin/php/php5.4.16/ext/php_sqlsrv_53_ts.dll

When you install third-party extensions you need to make sure that all the compilation parameters match:

• PHP version
• Architecture (32/64 bits)
• Compiler (VC9, VC10, VC11...)
• Thread safety

Common glitches includes:

• Editing the wrong php.ini file (that's typical with bundles); the right path is shown in phpinfo().
• Forgetting to restart Apache.

• Not being able to see the startup errors; those should show up in Apache logs, but you can also use the command line to diagnose it, e.g.:

  php -d display_startup_errors=1 -d error_reporting=-1 -d display_errors -c "C:\Path\To\php.ini" -m
  

If everything's right you should see sqlsrv in the command output and/or phpinfo() (depending on what SAPI you're configuring):

[PHP Modules]
bcmath
calendar
Core
[...]
SPL
sqlsrv
standard
[...]

If you are using Microsoft Drivers 3.1, 3.0, and 2.0. Please check your PHP version already install with IIS.

Use this script to check the php version:

<?php echo phpinfo(); ?>

OR

If you have installed PHP Manager in IIS using web platform Installer you can check the version from it.

Then:
If you are using new PHP version (5.6) please download Drivers from here

For PHP version Lower than 5.6 - please download Drivers from here

• PHP Driver version 3.1 requires PHP 5.4.32, or PHP 5.5.16, or later.
• PHP Driver version 3.0 requires PHP 5.3.0 or later. If possible, use PHP 5.3.6, or later.
• PHP Driver version 2.0 driver works with PHP 5.2.4 or later, but not with PHP 5.4. If possible, use PHP 5.2.13, or later.

Then use the PHP Manager to add that downloaded drivers into php config file.You can do it as shown below (browse the files and press OK). Then Restart the IIS Server

If this method not work please change the php version and try to run your php script.

Tip:Change the php version to lower and try to understand what happened.then you can download relevant drivers.