Which PHP function would you use to check if a string contains valid PHP code?

Using the eval() function in PHP executes a string of PHP code. While it does not explicitly validate if the code is valid before execution, it can be used to execute and thus attempt to run a string of PHP code.

If the string contains valid PHP syntax, it will execute without errors. However, if the string contains invalid syntax, it will generate a parse error. Thus, while eval() can indirectly help ascertain the validity of the PHP code, it executes the code, which means it should be handled with caution to avoid potential security vulnerabilities.

The other options provided—such as is_valid_php(), check_code(), and validate_php()—do not exist as built-in PHP functions and therefore cannot be used for the intended purpose of checking or validating PHP code. Hence, eval() is the only function that comes close to addressing the question, even though it's essential to note that using it requires careful consideration of the input to prevent executing unsafe or malicious code.