Functions

Functions, both ones built into PHP and ones you define yourself, make coding much easier - they take away lots of hard work because you can reuse other people's code, and they allow you to keep your scripts shorter and easier to maintain. As PHP 5 includes more than 2,500 functions, you might assume it's a very easy language indeed, but the truth is that each function needs to be used in different ways and so needs to be learnt individually. In this chapter you will learn your first PHP functions, with the most helpful and easy first.

Rather than writing pieces of code time after time whenever you want to execute the same functionality, PHP allows you to encapsulate code into a named function that you can call from elsewhere in your script.

PHP comes with hundreds of predefined functions that perform all manner of tasks from reading files and manipulating strings up to querying databases and connecting to an IRC server. If you find something is missing, you can add your own functions on a script by script basis, and these are called user functions .

In this section we will be covering a variety of the most important basic functions in PHP - more specialised functions can be found spread throughout the book under various sections, and should be looked up using the index.

Topics covered in this chapter are:

• Working with date and time

• Mathematical functions

• String manipulation

• Creating data hashes

• Regular expressions

• Extension handling

• Writing your own functions

• Recursive, variable, and callback functions

Chapter contents

1. 4.1. Functions overview
2. 4.2. How to read function prototypes
3. 4.3. Working with variables
4. 4.4. Controlling script execution
5. 4.5. Working with Date and Time
1. 4.5.1. Reading the current time
2. 4.5.2. Converting from a string
3. 4.5.3. Converting to a string
4. 4.5.4. Converting from components
6. 4.6. Mathematics
1. 4.6.1. Rounding
2. 4.6.2. Randomisation
3. 4.6.3. Trigonometrical conversion
4. 4.6.4. Other mathematical conversion functions
5. 4.6.5. Base conversion
6. 4.6.6. Mathematical constants
7. 4.7. Playing with strings
1. 4.7.1. Reading from part of a string
2. 4.7.2. Replacing parts of a string
3. 4.7.3. Converting to and from ASCII
4. 4.7.4. Measuring strings
5. 4.7.5. Finding a string within a string
6. 4.7.6. Returning the first occurrence of a string
7. 4.7.7. Trimming whitespace
8. 4.7.8. Wrapping your lines
9. 4.7.9. Changing string case
10. 4.7.10. Making a secure data hash
11. 4.7.11. Alternative data hashing
12. 4.7.12. Automatically escaping strings
13. 4.7.13. Pretty-printing numbers
14. 4.7.14. Removing HTML from a string
15. 4.7.15. Comparing strings
16. 4.7.16. Padding out a string
17. 4.7.17. Complex string printing
18. 4.7.18. Parsing a string into variables
8. 4.8. Regular expressions
1. 4.8.1. Basic regexps with preg_match() and preg_match_all()
2. 4.8.2. Novice regexps
3. 4.8.3. Advanced regexps
4. 4.8.4. Guru regexps
5. 4.8.5. Regular expression replacements
6. 4.8.6. Regular expression syntax examples
7. 4.8.7. The regular expressions coach
9. 4.9. Checking whether a function is available
10. 4.10. Extension functions
11. 4.11. Pausing script execution
12. 4.12. Executing external programs
13. 4.13. Connection-related functions
14. 4.14. Altering the execution environment
15. 4.15. User functions
1. 4.15.1. Return values
2. 4.15.2. Parameters
3. 4.15.3. Passing by reference
4. 4.15.4. Returning by reference
5. 4.15.5. Default parameters
6. 4.15.6. Variable parameter counts
16. 4.16. Variable scope in functions
17. 4.17. Overriding scope with the GLOBALS array
18. 4.18. Recursive functions
19. 4.19. Variable functions
20. 4.20. Callback functions
21. 4.21. The declare() function and ticks
22. 4.22. Handling non-English characters
23. 4.23. Undocumented functions
24. 4.24. Summary
25. 4.25. Exercises
26. 4.26. Further reading
27. 4.27. Next chapter

Follow us on Identi.ca or Twitter