#What does empty mean in php?
empty means empty, it is a built-in function in php, used to check whether a variable is empty.
empty() Determines whether a variable is considered empty. When a variable does not exist, or its value is equal to FALSE, then it is considered not to exist. empty() does not generate a warning if the variable does not exist.
empty() After version 5.5, it supports expressions, not just variables.
Version requirements: PHP 4, PHP 5, PHP 7
Basic syntax:
empty ( $var )
Parameters: empty() The function accepts a single argument, as shown in the syntax above, as described below.
$ var: Variable used to check if it is empty.
Return value: Return false when $var exists and has a non-null non-zero value. Otherwise return true.
Note: Under PHP 5.5, the empty() function only supports variable checking, and anything else will cause a parsing error.
Simple example of empty() function
Let’s use an example to introduce how the empty() function uses to determine whether a variable is empty
<?php header("content-type:text/html;charset=utf-8"); echo "<br>"; $var1 = NULL; $var2 = ""; $var3 = "PHP中文网"; empty($var1) ? print_r("变量var1为空<br>") : print_r("变量var1不为空<br>"); empty($var2) ? print_r("变量var2为空<br>") : print_r("变量var2不为空<br>"); empty($var3) ? print_r("变量var3为空<br>") : print_r("变量var2不为空,值为:".$var3); ?>
Output:
Explanation:
The following will be used by the empty() function Values considered null:
1, "" (empty string)
2, 0 (0 as an integer)
3, 0.0 (0 as a floating point number )
4, "0" (0 as a string)
5, null
6, false
7, array() (an empty Array)
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php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($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。

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。

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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