


There are many functions with similar functions in PHP, but there are subtle differences. As analyzed in this article, the three functions of is_null, empty, and isset are not easy to implement without a lot of effort. Got it! Let’s follow the webmaster to learn more about the differences between these three functions!
Let’s first take a look at the functional descriptions of these three functions
isset determines whether the variable already exists. If the variable exists, it returns TRUE, otherwise it returns FALSE.
empty determines whether the variable is empty. If the variable is a non-empty or non-zero value, empty() returns FALSE. In other words, "", 0, "0", NULL, FALSE, array(), var $var; and objects without any attributes will be considered empty, and TRUE will be returned if the variable is empty.
is_null determines whether the variable is NULL
How about this? This explanation is generally used, but this explanation is already very confusing. Let’s analyze it with specific examples below!
From this we can find that as long as the variable is "" or 0, or false or null, empty will return true as long as these values are.
isset only determines whether the variable exists. As long as your variable is not null or unassigned, the return result will be true. If you use isset() to test a variable that is set to NULL, it will return FALSE. Also note that a NULL byte ("
And is_null is exactly the inverse result of isset. We can think of it as !isset, which is an inverse operation of isset.From the above examples, we can also draw the following conclusions (which will be often used in programming in the future):
Assume $var is any type
When empty($var) is true, (bool)($var) is false. vice versa.
When is_null($var) is true, isset($var) is false. vice versa.
For example:
$i=$j+1;
Here is_null($j) is true (it can be understood that isset($j) is false, because the variable $j is not declared in advance)
Two other points to note are :
(1) empty() only detects variables, and detecting anything that is not a variable will result in a parsing error. In other words, the following statement will not work: empty(addslashes($name)).(2) isset() can only be used for variables, because passing any other parameters will cause a parsing error. If you want to check whether a constant has been set, use the defined() function. Articles you may be interested in
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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。

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。

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。

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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