How to get the first digits of a string in php

This article mainly introduces the method of obtaining the first few characters of a string in PHP. Interested friends can refer to it. I hope it will be helpful to everyone.

In actual project applications, it is often encountered using php to obtain the first few digits of a string for comparison, assignment, etc. Today I will share with you how to use php substr to get the first few digits, last digits, and specified position of a string.

substr

(PHP 4, PHP 5)

substr — Returns a substring of a string

Description

string substr (string $string, int $start [, int $length])

Returns the substring of string string specified by the start and length parameters.

Parameters

string

Input string.

start

If start is a non-negative number, the returned string will start from the start position of string and start counting from 0. For example, in the string "abcdef", the character at position 0 is "a", the character at position 2 is "c", and so on.

If start is a negative number, the returned string will start from the start character forward from the end of string.

If the length of string is less than or equal to start, FALSE will be returned.

Example #1 Use negative start

<?php
$rest = substr(“abcdef”, -1); // 返回 “f”
$rest = substr(“abcdef”, -2); // 返回 “ef”
$rest = substr(“abcdef”, -3, 1); // 返回 “d”
?>

##length

Example #2 Use negative length

<?php
$rest = substr(“abcdef”, 0, -1); // 返回 “abcde”
$rest = substr(“abcdef”, 2, -1); // 返回 “cde”
$rest = substr(“abcdef”, 4, -4); // 返回 “”
$rest = substr(“abcdef”, -3, -1); // 返回 “de”
?>

Example #3 basic usage of substr()

<?php
echo substr(‘abcdef&#39;, 1); // bcdef
echo substr(‘abcdef&#39;, 1, 3); // bcd
echo substr(‘abcdef&#39;, 0, 4); // abcd
echo substr(‘abcdef&#39;, 0, 8); // abcdef
echo substr(‘abcdef&#39;, -1, 1); // f

// 访问字符串中的单个字符
// 也可以使用中括号
$string = ‘abcdef&#39;;
echo $string[0]; // a
echo $string[3]; // d
echo $string[strlen($string)-1]; // f
?>

Example #4 substr() casting behavior

<?php
class apple {
public function __toString() {
return “green”;
}
}

echo “1) “.var_export(substr(“pear”, 0, 2), true).PHP_EOL;
echo “2) “.var_export(substr(54321, 0, 2), true).PHP_EOL;
echo “3) “.var_export(substr(new apple(), 0, 2), true).PHP_EOL;
echo “4) “.var_export(substr(true, 0, 1), true).PHP_EOL;
echo “5) “.var_export(substr(false, 0, 1), true).PHP_EOL;
echo “6) “.var_export(substr(“”, 0, 1), true).PHP_EOL;
echo “7) “.var_export(substr(1.2e3, 0, 4), true).PHP_EOL;
?>

The above routine will output:

2) '54'
3) 'gr'
4) '1'
5) false
6) false
7) '1200'

<?php
var_dump(substr(‘a&#39;, 1)); // bool(false)
?>

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