


Characters in php are abstract entities that can be represented using a variety of different character schemes or code pages. A byte is a unit for transmitting information over a network (or storing information on a hard drive or in memory). This article also introduces examples of string and byte conversion in PHP through examples. Friends who are interested should take a look together
Characters:
Characters are abstract entities that can be represented using many different character schemes or code pages. For example, Unicode UTF-16 encoding represents characters as a sequence of 16-bit integers, while Unicode UTF-8 encoding represents the same characters as a sequence of 8-bit bytes. The common language runtime uses Unicode UTF-16 (Unicode Transformation Format, a 16-bit encoding) to represent characters.
In php, under UTF-8 encoding, a Chinese character occupies 3 characters, and under gbk encoding, it only occupies 2 characters.
Byte (Byte):
Byte is to transmit information through the network (or store information on the hard disk or memory) The unit.
Application:
If the table in the database is UTF8 encoded, and the field is set to a maximum of 10 characters, the maximum storage length is eg: 'I am in 1'
Let’s look at the PHP string and byte conversion example
<?php /** * byte数组与字符串转化类 */ class Bytes { /** * 转换一个String字符串为byte数组 * @param $str 需要转换的字符串 * @param $bytes 目标byte数组 * @author Zikie */ public static function getBytes($string) { $bytes = array(); for($i = 0; $i < strlen($string); $i++){ $bytes[] = ord($string[$i]); } return $bytes; } /** * 将字节数组转化为String类型的数据 * @param $bytes 字节数组 * @param $str 目标字符串 * @return 一个String类型的数据 */ public static function toStr($bytes) { $str = ''; foreach($bytes as $ch) { $str .= chr($ch); } return $str; } /** * 转换一个int为byte数组 * @param $byt 目标byte数组 * @param $val 需要转换的字符串 * */ public static function integerToBytes($val) { $byt = array(); $byt[0] = ($val & 0xff); $byt[1] = ($val >> 8 & 0xff); $byt[2] = ($val >> 16 & 0xff); $byt[3] = ($val >> 24 & 0xff); return $byt; } /** * 从字节数组中指定的位置读取一个Integer类型的数据 * @param $bytes 字节数组 * @param $position 指定的开始位置 * @return 一个Integer类型的数据 */ public static function bytesToInteger($bytes, $position) { $val = 0; $val = $bytes[$position + 3] & 0xff; $val <<= 8; $val |= $bytes[$position + 2] & 0xff; $val <<= 8; $val |= $bytes[$position + 1] & 0xff; $val <<= 8; $val |= $bytes[$position] & 0xff; return $val; } /** * 转换一个shor字符串为byte数组 * @param $byt 目标byte数组 * @param $val 需要转换的字符串 * */ public static function shortToBytes($val) { $byt = array(); $byt[0] = ($val & 0xff); $byt[1] = ($val >> 8 & 0xff); return $byt; } /** * 从字节数组中指定的位置读取一个Short类型的数据。 * @param $bytes 字节数组 * @param $position 指定的开始位置 * @return 一个Short类型的数据 */ public static function bytesToShort($bytes, $position) { $val = 0; $val = $bytes[$position + 1] & 0xFF; $val = $val << 8; $val |= $bytes[$position] & 0xFF; return $val; } } ?>
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php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($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。

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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