Step by step learn PHP of 3 PHP functions

2020-03-31 20:20:14
OfStack
1. Method overview



First, write a simple function that you can look at:

< Html>
< Head>
< Title> HelloPHP< / title>
< / head>
< Body>
< ? PHP
The function CustomPrint ($STR)
{
For ($I = 0; $i< 5; $i++)
{
Echo ($STR);
Echo (' < Br / > ');
}
}
CustomPrint (" Hello ");
? >
< / body>
< / html>


(link: http://11011.net/software/vspaste)

With this example, I'm sure you've all learned a little bit about how functions are written in PHP, but as far as syntax is concerned, it's not that different from other c-like languages. It's all while,for,if, and so on.

OK, so let me summarize the main points of this method:

A. PHP's method is declared with function, which is similar to the familiar Javascript.

B. Variables must begin with a dollar character ($).



2. Parameter reference passing and value passing



Parameter value transfer and reference transfer, I believe that everyone has been exposed to C language when learning, here use C# to write an example:

Public void Swap(int a, int b)
{
Int temp = a;
A = b;
B = temp.
}
Public void Swap(ref int a, ref int b)
{
Int temp = a;
A = b;
B = temp.
}


(link: http://11011.net/software/vspaste)

So let's write a PHP version here.

< ? PHP
The function Swap1 ($a, $b)
{
$temp = $a;
$a = $b;
$b = $temp;
}
The function Swap2 (& $a, & $b)
{
$temp = $a;
$a = $b;
$b = $temp;
}
The function CustomPrint ($STR)
{
Echo ($STR);
Echo (" < Br / >" );
}
$a = 1;
$b = 2;
Swap1 ($a, $b);
CustomPrint(" result of value passed :");
CustomPrint (' $a = '$a);
CustomPrint (' $b = '$b);
$a = 1;
$b = 2;
Swap2 ($a, $b);
CustomPrint(" result passed by reference :");
CustomPrint (' $a = '$a);
CustomPrint (' $b = '$b);
? >
(link: http://11011.net/software/vspaste)




In this example: there are two points I need to make:

A. The difference between value passing and reference passing is the "&" before the parameter.

B. CustomPrint (' $a = '$a); The only difference between single and double quotation marks is that the variable name can be resolved.

< ? PHP
$a = 1;
Echo (" $a ");
Echo (" < Br / >" );
Echo (" $a ");
? >
(link: http://11011.net/software/vspaste)


 

(link: https://www.jb51.net/upload/2010-2/20100215135132775.png)  

Finally, with respect to performance, PHP needs to copy and then pass when passing by value, so that those large objects or strings are not only time consuming, but also a waste of space. At this point, if you pass by reference, you save yourself the performance penalty of copying. Good for performance.



3. Scope issues



In C#, because variables must be declared before they can be used, there is a concept of scope and subscope, which is not available in PHP.

Let's take a look at some C# code:

Public class Student
{
Private string name;
Public void SayHello ()
{
HttpContext. Current. The Response. The Write (" Hello, I am "+ name);
}
}


(link: http://11011.net/software/vspaste)

That is, you can access variables declared by an external class in a method, but not in PHP:

< ? PHP
$name = "kym";
The function SayHello ()
{
If (isset ($name))
{
Echo (" Hello $name ");
}
The else
{
Echo (" $name is undefined ");
}
}
SayHello ();
? >


(link: http://11011.net/software/vspaste)

(link: https://www.jb51.net/upload/2010-2/20100215135132951.png)

Here is a function called "isset" that detects whether a variable is defined or whether it is an empty string.

This result indicates that the external variable $name cannot be accessed in the body of the function.

Here is a bit more: a function corresponding to unset: unset. This function removes the value of a variable.

Write a simple example:

< ? PHP
$name = "kym";
If (isset ($name))
{
Echo (" Yes ");
}
The else
{
Echo (" No ");
}
The unset ($name);
If (isset ($name))
{
Echo (" Yes ");
}
The else
{
Echo (" No ");
}
? > (link: http://11011.net/software/vspaste)

 

(link: https://www.jb51.net/upload/2010-2/20100215135132413.png)

These will be mentioned in more detail in the garbage collection later.