PHP is one of the most popular languages for creating websites. One of its strengths is the availability of a huge number of built-in functions that allow you to perform even complex operations in literally one line of code.
What are built-in functions?
These are functions that are already included in the language and are available immediately after installing PHP — without the need to write additional code or connect third-party libraries. They cover a wide range of tasks: from working with strings and arrays to processing files, dates, and interacting with the server.
But there are nuances: functions require extensions
Not all functions are equally accessible. Some require additional extensions, without which PHP will not be able to execute them. For example:
- Working with images requires the GD extension.
- Connecting to MySQL databases requires MySQLi or PDO MySQL.
If the required extension is not installed or active, attempting to use such a function will result in a fatal error — PHP simply will not recognize it.
You can find out which extensions are available in your environment using built-in tools:
- phpinfo() — displays complete information about the PHP configuration.
- get_loaded_extensions() — shows a list of loaded extensions.
Which functions are available “out of the box”?
Many built-in functions are always available, without additional dependencies. Here are some of the most useful categories:
Working with strings
- strlen() — counts the number of characters in a string.
- str_replace() — replaces one substring with another.
- substr() — extracts part of a string.
Working with variables
- isset() — checks whether a variable has been set.
- empty() — checks whether a variable is empty.
- var_dump() — displays information about the type and content of a variable.
Working with arrays
- array_merge() — merges arrays.
- in_array() — checks whether an element is in an array.
- array_map() — applies a function to all elements of an array.
Date and time
- time() — returns the current time in UNIX format.
- date() — formats a timestamp into a convenient form.
- strtotime() — converts a date string into a timestamp.
Working with files
- file_get_contents() — reads the contents of a file.
- file_put_contents() — writes data to a file.
- fopen(), fwrite(), fclose() — more flexible file handling.
How to read function documentation
If you want to use PHP’s built-in functions effectively, learn how to read the official documentation. It specifies:
- What parameters the function accepts.
- What it returns — for example, the result of the operation or false in case of an error.
- Whether it modifies the passed values.
- From which PHP version the function is available.
Important notes on usage and pitfalls.
Example: str_replace() returns a new string without changing the original, while usort() changes the array passed to it — this is important to consider in order to avoid unpredictable behavior.
Why it is important to know the built-in functions
- Less code — no need to write from scratch what has already been implemented.
- Performance — built-in functions are optimized and work faster than user solutions.
- Reliability — they are well tested and widely used.
- Compatibility — many hosting providers only support a standard set of extensions, so it’s better to rely on out-of-the-box functions.
Conclusion
Learning PHP’s built-in functions is one of the most effective ways to improve your programming skills and write clean, readable, and reliable code. The better you know them, the easier and faster you can solve typical tasks.