Summary of commonly used character functions in php

This article mainly introduces the common character functions in PHP, and summarizes and analyzes the common character functions substr, preg_match, strpos, dirname and str_split in PHP in the form of examples. The functions, usage and related Notes, friends in need You can refer to the following examples

This article summarizes common character functions in PHP. Share it with everyone for your reference, the details are as follows:

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

Function function: Return the substring of the string string specified by the start and length parameters.

Parameters:

string: Enter the character 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 'abcdef', position 0 is 'a' and position 2 is 'c ';
If start is a negative number, the returned string will start from the start character forward from the end of the string.
If the length of string is less than or equal to start, return FALSE.

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

$length: If a positive length is provided, the returned string will contain at most length characters from start (depending on the length of the string).

If a negative length is provided, many characters at the end of the string will be missed, that is, characters will not be considered from the end (you can understand that I truncate). If start is not in the text, then a will be returned Empty string.

If length is provided with a value of 0, FALSE or NULL, an empty string will be returned.

If length is not provided, the returned string will be from the start position to the end of the character.

$rest=substr("abcdef","0","-1");  //返回 abcde
$rest=substr("abcdef","2","-1");  //返回 cde
$rest=substr("abcdef"," 4","-4"); //返回 NULL
$rest=substr("abcdef","-3","-1"); //返回 de

[ ] The square brackets indicate that the parameter is optional. If not set, it will be the default parameter. (I have been working with PHP for almost 8 months, and I have always wondered why function parameters need to be enclosed in square brackets. Today I finally couldn’t help but Baidu! Shame!)

2. int preg_match(string $pattern, string $subject [, array &$matches [, int $flag=0 [, int $offset=0 ]]])

Function : Search for a match between subject and the regular expression given by pattern.

Parameters:

$pattern: Pattern to be searched, Character type.
$subject: Input string.
$matches: If the parameter matches is provided, it will be populated as the search results, $matches[0] contains the text matched by the complete pattern, $matches[1] will contain the first capture Subgroups match text, and so on.
$flags :flags can be set to the following tag values:

PREG_OFFSET_CAPTURE

If this flag is passed, for each occurrence Matches are returned with the string offset (relative to the target string) appended. Note: This will change the array populated in the matches argument so that each element becomes a string whose 0th element is the matched string. , the first element is the offset of the matching string in the target string subject.

offset:

Usually, the search starts from the beginning of the target string Unknown start. The optional parameter offset is used to specify the search starting from an unknown point in the target string (unit is byte).

Note:

Use the offset parameter It is different from passing to preg_match() the result of intercepting the target string according to the position through substr($subject, $offset), because pattern can contain assertions such as ^,$ or (?<=x). Comparison:

<?php
$subject = "abcdef";
$pattern = &#39;/^def/&#39;;
preg_match($pattern, $subject, $matches, PREG_OFFSET_CAPTURE, 3);
print_r($matches);
?>

The above routine will output:

Array
(
)

<?php
$subject = "abcdef";
$pattern = &#39;/^def/&#39;;
preg_match($pattern, substr($subject,3), $matches, PREG_OFFSET_CAPTURE);
print_r($matches);
?>

will produce a match

Array
(
  [0] => Array
    (
      [0] => def
      [1] => 0
    )
)

3. strpos(string,find,start)

string: Required, specifies the string to be searched.
find: Required, specifies the characters to be found.
start: Optional, specifies the position to start the search, starting from the first character by default.

This function is case-sensitive. If you do not want this, you can use the stripos() function

Example:

echo strpos("Hello  world! "," wo ");// 输出 6

4. string dirname(string path)

Function: Get the directory name in the path. In Win32 systems, you can use slashes (/) or backslashes (\); but in other operating systems, the paths are (/).

$path = "/etc/hostname";
$file = dirname($path);

$file is "/etc"

5. str_split(string,length)

string 必需。规定要分割的字符串。
length 可选。规定每个数组元素的长度。默认是 1。

<?php
print_r(str_split("Hello"));
?>

运行结果：

Array
(
[0] => H
[1] => e
[2] => l
[3] => l
[4] => o
)

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