The meaning of reference in PHP is: different names access the same variable content. There is a difference between
and pointers in C language. The pointer in C language stores the address of the variable's content in memory
Variable reference
PHP's reference allows you to use two variables to point to the same content
$a="ABC";
$b =&$ a;
echo $a;//Output here: ABC
echo $b;//Output here: ABC
$b="EFG";
echo $a;//Here $a The value becomes EFG so output EFG
echo $b;//Output EFG here
?>
Pass-by-reference call of function
Pass I won’t say much about the address call. The code is given directly below:
function test(&$ a)
{
$a=$a+100;
}
$b=1;
echo $b;//output 1
test($b); / /What $b is passed to the function here is actually the memory address where the variable content of $b is located. By changing the value of $a in the function, the value of $b can be changed
echo "
";
echo $b;//Output 101
It should be noted that if test(1); is used here, an error will occur. Think about the reason yourself.
The reference return of the function
Look at the code first
function &test()
{
static $b=0;//Declare a static variable
$b=$b+1;
echo $b;
return $b;
}
$a=test ();//This statement will output the value of $b as 1
$a=5;
$a=test();//This statement will output the value of $b as 2
$a=&test();//This statement will output the value of $b as 3
$a=5;
$a=test();//This statement will output the value of $b as 6
Explain below:
In this way $a=test(); what you get is not actually a function reference return, which is no different from an ordinary function call. As for the reason: This is PHP regulations
PHP stipulates that what is obtained through $a=&test(); is the reference return of a function
As for what is a reference return (the PHP manual says: reference return is used when you want to use a function to find a reference Which variable should be bound to. ) I couldn’t understand this nonsense for a long time
Using the above example to explain it is that
$a=test() calls the function, which just assigns the value of the function to $a, and $a does anything The changes will not affect $b in the function
. If the function is called through $a=&test(), its function is to compare the memory address of the $b variable in return $b with the memory address of the $a variable. Pointing to the same place
produces the equivalent effect ($a=&b;), so changing the value of $a also changes the value of $b, so after executing
$a=&test() ;
$a=5;
After that, the value of $b becomes 5
The static variable is used here to let everyone understand the reference return of the function. In fact, the reference return of the function is mostly used in objects
Object reference
class a{
var $abc="ABC";
}
$b=new a;
$c=$b;
echo $b->abc;//output here ABC
echo $c->abc;//Output ABC here
$b->abc="DEF";
echo $c->abc;//Output DEF here
?>
The above code is the running effect in PHP5
In PHP5, the copying of objects is achieved through references. In the above column, $b=new a; $c=$b; is actually equivalent to $b=new a; $c=&$b;
The default in PHP5 is to call objects by reference, but sometimes you may want to Create a copy of an object and hope that changes to the original object will not affect the copy. For this purpose, PHP defines a special method called __clone.
The role of reference
If the program is relatively large, there are many variables referencing the same object, and you want to manually clear the object after using it, I personally recommend using the "&" method, and then using $var=null to clear it. Other times, use php5. The default method. In addition, for transferring large arrays in php5, it is recommended to use the "&" method, after all, it saves memory space.
Unreference
When you unset a reference, you just break the binding between the variable name and the variable content. This does not mean that the variable contents are destroyed. For example:
$a = 1;
$ b =& $a;
unset ($a);
?>
Won’t unset $b, just $a.
global reference
When you declare a variable with global $var you actually create a reference to the global variable. In other words, it is the same as doing this:
$ var =& $GLOBALS["var"];
?>
This means, for example, that unset $var will not unset a global variable.
$this
In a method of an object, $this is always a reference to the object that calls it.
//Here’s another little episode
The pointing (similar to pointer) function of the address in PHP is not implemented by the user himself, but is implemented by the Zend core. The reference in PHP uses "write The principle of "time-copy" is that unless a write operation occurs, variables or objects pointing to the same address will not be copied.
In layman terms
1: If there is the following code
$a="ABC";
$b=$a;
In fact, $a and $b point to the same point at this time The memory address is not that $a and $b occupy different memories
2: If you add the following code to the above code
$a="EFG";
Because $a and $b The data in the pointed memory needs to be rewritten. At this time, the Zend core will automatically determine and automatically produce a data copy of $a for $b, and re-apply for a piece of memory for storage.

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

查找方法:1、用strpos(),语法“strpos("字符串值","查找子串")+1”;2、用stripos(),语法“strpos("字符串值","查找子串")+1”。因为字符串是从0开始计数的,因此两个函数获取的位置需要进行加1处理。


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