What is the purpose of the json_encode() function in PHP?

The json_encode() function in PHP is used specifically to convert a PHP array or object into a JSON string. This is particularly useful when you need to exchange data between a server and a client in a format that can be easily understood and used by both. JSON (JavaScript Object Notation) is a lightweight data interchange format that is easy for humans to read and write, and easy for machines to parse and generate.

When you call json_encode() with a PHP array or object as an argument, the function processes the data structure and generates a corresponding JSON string. This transformation allows data from the PHP back-end, such as user information or database records, to be sent to a JavaScript front-end or any other system that understands JSON.

The other options deal with different aspects of JSON handling in PHP. For instance, decoding a JSON string into a PHP array or object is conducted using the json_decode() function, not json_encode(). Validation of JSON syntax does not pertain specifically to the json_encode() function but rather involves checking if a string conforms to the JSON format. Sending JSON data to a client is more a matter of ensuring that the appropriate headers are set and the content is transmitted correctly, which is not the primary role of json_encode().