words :: includes and functions

includes and functions

24 Jan 08

the usefulness of reusing code should be obvious to everyone!
require() and include() call code from a file
the main difference is that if something goes wrong, require() will return a fatal error, include() will only give a warning
data need not be passed to the include because it is inserted in the code and executed as if present all along (I think)
it’s a good idea to store include files outside the document tree, making them invisible to internet interlopers

“A function is a self-contained module of code that prescribes a calling interface, performs some task, and optionally returns a result”
a library of user-defined functions can be stored in an include file
data must be passed to a function using a parameter (see “scope”, below)
user-defined functions must be declared, e.g.

function say_hi() { echo 'hi'; }

function names can only contain letters, digits, underscores; cannot begin with a digit; and cannot be the same as an existing function name

scope controls where a variable is visible and useful
variables declared inside a function are in scope from the declaration until the function’s end brace; this is function scope, the variables are local variables
variables declared outside functions are in scope from the declaration to the end of the file, but not inside functions; this is global scope, the variables are global variables
if a require() or include() statement is used within a function, function scope applies; if not, global
the keyword global can be used to give a variable defined within a function global scope
to allow functions to operate on global variables, use a pass by reference; the function receives a reference to the original variable, and any modifications performed on the reference are also performed on the original
a pass by reference is created by prefixing an ampersand to the variable name in the function’s parameter list
the return keyword can be used to stop a function, usually in response to some condition; return can also be used to return a value
it is possible to call a function recursively, but this seems dangerous and doesn’t appear to have many benefits

Welling, Luke and Laura Thomson. PHP and MySQL Web Development. 2nd ed. Indianapolis: Sam’s, 2003.

Posted by pzed on January 24, 2008 at 4.55pm
Categories: libraries, music, web stuff