How to determine if PDO is enabled in PHP?

The proper way of determining that will be using the extension_loaded function:-

if ( extension_loaded('pdo') ) {
    .......
}

And you might also want to check for the database-specific PDO driver using:-

if ( extension_loaded('pdo_<database type here>') ) { // e.g., pdo_mysql
    .......
}

~~Check if the class exists:~~

if (class_exists('PDO'))

I appreciate the support and all the upvotes I still get, but please check Salman Abbas's answer for the proper way to do this.

Just run the command as php -m from the command prompt which will display list of modules installed for PHP

You have two options:

if (extension_loaded('pdo')) { /* ... */ }

Or (this one is not 100% reliable since it can be implemented in user-land classes):

if (class_exists('PDO', false)) { /* ... */ }

Personally, I prefer the first option.

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