 The foreach Loop | PHP Programming Functions | PHP Include Files |
Functions (ormethods in the context of a class/object) are a way to group common tasks or calculations to be re-used simply.
Functions in computer programming are much like mathematical functions: You can give the function values to work with and get a result without having to do any calculations yourself.
You can also find a huge list of predefined functions built into PHP in thePHP Manual's function reference.
Note thatecho is not a function.[1]"Calling a function" means causing a particular function to run at a particular point in the script. The basic ways to call a function include:
print('I am human, I am.');
if($a==72){print('I am human, I am.');}
$result=sum($a,5);
while($i<count($one)){}
In our earlier examples we have called several functions. Most commonly we have called the functionprint() to print text to the output. The parameter for echo has been the string we wanted printed (for exampleprint("Hello World!") prints "Hello World!" to the output).
If the function returns some information, we assign it to a variable with a simple assignment operator "=":
$var1=func_name();
Parameters are variables that exist only within that function. They are provided by the programmer when the function is called and the function can read and change them locally (except for reference type variables that are changed globally, which is a more advanced topic).
When declaring or calling a function that has more than one parameter, you need to separate between different parameters with a comma ','.
A function declaration can look like this:
functionprint_two_strings($var1,$var2){echo$var1;echo"\n";echo$var2;returnNULL;}
To call this function, you must give the parameters a value. It doesn't matter what the value is, as long as there is one:
print_two_strings("Hello","World");
Output:
HelloWorld
When declaring a function, you sometimes want to have the freedom not to use all the parameters. Therefore, PHP allows you to give them default values when declaring the function:
functionprint_two_strings($var1="Hello World",$var2="I'm Learning PHP"){echo($var1);echo("\n");echo($var2);}
These values will only be used, if the function call does not include enough parameters. If there is only one parameter provided, then$var2 = "I'm Learning PHP":
print_two_strings("Hello");
Output:
HelloI'm Learning PHP
Another way to have a dynamic number of parameters is to use PHP's built-infunc_num_args,func_get_args, andfunc_get_arg functions.
functionmean(){$sum=0;$param_count=func_num_args();for($i=0;$i<$param_count;$i++){$sum+=func_get_arg($i);}$mean=$sum/$param_count;echo"Mean:{$mean}";returnNULL;}
or
functionmean(){$sum=0;$vars=func_get_args();for($i=0;$i<count($vars);$i++){$sum+=$vars[$i];}$mean=$sum/count($vars);echo"Mean:{$mean}";returnNULL;}
The above functions would calculate thearithmetic mean of all of the values passed to them and output it. The difference is that the first function usesfunc_num_args andfunc_get_arg, while the second usesfunc_get_args to load the parameters into an array. The output for both of them would be the same. For example:
mean(35,43,3);
Output:
Mean: 27
This function is all well and good, but usually you will want your function to return some information. Generally there are two reasons why a programmer would want information from a function:
To return a value from a function use thereturn() statement in the function.
functionadd_numbers($var1=0,$var2=0,$var3=0){$var4=$var1+$var2+$var3;return$var4;}
Example PHP script:
functionadd_numbers($var1=0,$var2=0,$var3=0){$var4=$var1+$var2+$var3;return$var4;}$sum=add_numbers(1,6,9);echo"The result of 1 + 6 + 9 is{$sum}";
Result:
The result of 1 + 6 + 9 is 16
Notice that areturn() statement ends the function's course. If anything appears in a function declaration after thereturn() statement is executed, it is parsed but not executed. This can come in handy in some cases. For example:
functiondivide($dividee,$divider){if($divider==0){// Can't divide by 0.returnfalse;}$result=$dividee/$divider;return$result;}
Notice that there is noelse after theif. This is due to the fact that, if$divider does equal0, thereturn() statement is executed and the function stops.
If you want to return multiple variables, you need to return an array rather than a single variable. For example:
functionmaths($input1,$input2){$total=($input1+$input2);$difference=($input1-$input2);$return=array("tot"=>$total,"diff"=>$difference);return$return;}
When calling this from your script, you need to call it into an array. For example:
$return=maths(10,5);
In this case$return['tot'] will be the total (e.g. 15), while$return['diff'] will be the difference (5).
A developer can create functions inside a PHP script without having to use thefunction name($param...) {} syntax. This can be done by way of programming that can let you run functions dynamically.
There are two ways to do it: either using the direct call, or thecall_user_func or thecall_user_func_array:
call_user_func andcall_user_func_array only differ in that thecall_user_func_array allows you to use the second parameter as array to pass the data very easily, andcall_user_func has an infinite number of parameters that is not very useful in a professional way.In these examples, a class will be used for a wider range of using the example:
classSome_Class{functionmy_function($text1,$text2,$text3){$return=$text1."\n\n".$text2."\n\n".$text3;return$return;}}$my_class=newSome_Class();
Usingcall_user_func:
$one="One";$two="Two";$three="Three";$callback_func=array(&$my_class,"my_function");$result=call_user_func($callback_func,$one,$two,$three);echo$result;
Usingcall_user_func_array:
$one="One";$two="Two";$three="Three";$callback_func=array(&$my_class,"my_function");$result=call_user_func_array($callback_func,array($one,$two,$three));echo$result;
Note howcall_user_func andcall_user_func_array are used in both of the examples.call_user_func_array allows the script to execute the function more dynamically.
As there was no example of using both of these functions for a non-class function, here they are:
Usingcall_user_func:
$one="One";$two="Two";$three="Three";$callback_func="my_function";$result=call_user_func($callback_func,$one,$two,$three);echo$result;
Usingcall_user_func_array:
$one="One";$two="Two";$three="Three";$callback_func="my_function";$result=call_user_func_array($callback_func,array($one,$two,$three));echo$result;
$my_func($param1,$param2);$my_class_name=newClassObject();$my_class_name->$my_func_from_that_class($param1,$param2);// The -> symbol is a minus sign follow by a "larger than" sign. It allows you to// use a function that is defined in a different PHP class. It comes directly from// object-oriented programming. Via a constructor, a function of that class is// executable. This specific example is a function that returns no values.call_user_func($my_func,$param1,$param2);call_user_func(array(&${$my_class_name},$my_func),$param1,$param2);// Prefixing a & to a variable that represents a class object allows you to send the// class object as a reference instead of a copy of the object. In this example this// means that $my_class_name Object would have a copy made of it, the function will// act on the copy, and when the function ends. The original object wouldn't suffer// modifications. Passing an object through its reference passes the address in memory// where that object is stored and call_user_func will alter the actual object.call_user_func_array($my_func,array($param1,$param2));// Most powerful, dynamic examplecall_user_func_array(array(&${$my_class_name},$my_func),array($param1,$param2));
functionpositif($x+$y;){$x=2;$y=5;$z=$x+$y;echo$z;}positif=$x+$y;
Creating runtime functions is a very good way of making the script more dynamic:
$function_name=create_function('$one, $two','return $one + $two;');echo$function_name."\n\n";echo$function_name("1.5","2");
create_function creates a function with parameters$one and$two, with a code to evaluate return…Whencreate_function is executed, it stores the function's info in the memory and returns the function's name. This means that you cannot customise the name of the function although that would be preferred by most developers.
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