Summary of commonly used string manipulation functions in PHP

In the process of programming, string operations are very important and are often used. Common string operations include string splicing, string replacement, string search, string comparison, and copying. Strings and calculating the length of strings, etc.

1, Splicing strings
Splicing strings is one of the most commonly used string operations. PHP supports three ways to splice strings, namely dot and delimiter {} operations, There is also a dot equal sign.= to perform operations. The dot equal sign can decompose a relatively long string into several lines for definition, which is more beneficial.

2, replace the string
In the PHP language, a function called substr_replace() is provided. The function of this function can quickly complete the scanning and editing of string replacement functions with large text content. His Syntax format:
mixed substr_replace(mixed $string,string $replacement, int $start[,int $length])
Explanation of the above syntax format:
string is to be checked or to be replaced String
replacement specifies the string to be inserted or replaced
start specifies where to start replacement in the string. This parameter can take three types of values ​​(positive number: starting from the beginning of the string) Start replacing at the start offset, negative number, start replacing from the start offset at the end of the string, 0: start replacing from the first character in the string)
length specifies how many characters to replace, This parameter can also take three types of values ​​(positive number: the length of the string to be replaced, negative number: the length of the string to be replaced starting from the end of the string, 0: it is an insertion operation, not a replacement operation);

3, Calculate the string

1) Calculate the length of the string
In PHP, the strlen() function is used to calculate the length of the string and return the length information of the string The format of this syntax is as follows: int strlen(string $string) The string in the format is used to specify the string whose length is to be calculated.

2) Calculate the number of strings
In PHP,substr_count() function can be used to very conveniently and accurately determine how many specified substrings there are in the provided string. The syntax format of the substr_count() function is as follows: int substr_count(string $ haystack, string $needle[,int $offset=0[,int $length]]) The description of the parameters designed in the above syntax is as follows: haystack specifies the string to be checked, and needle is used to specify the string to be inserted. offset is used to specify where to start searching in the string, the default value is 0, and length is used to specify the length of the search.
In PHP, the str_word_count() function can be used very conveniently and To accurately determine how many words there are in the provided string, the syntax format of the str_word_count() function is as follows: mixed str_word_count(string $string[,int $format=0[,string $charlist]]) above The description of the parameters involved in the syntax is as follows: string is used to specify the string to be checked, format is used to specify the return value of str_word_count() function, the return value of this parameter can return three values , respectively 0, 1, 2. The return of 0 means the default value, which returns the number of words found. If the return value is 1, then str_word_count() returns an array in which the key names start from 0 Continuous integers, the value is the actual word. If the value of format is 3, then the return value of the str_word_count() function is an array, where the key of the array is the position of the word in the string, and the value is the actual word Word.

4, Searching for strings

Searching for strings can be divided into many types, such as finding substrings, finding the position of a certain string, etc., PHP provides each Corresponding functions are provided for string search operations.

1) Search for substrings
In PHP language, the strstr() function can be used to search for substrings, and the result returned by this function is substring All content that appears for the first time in a string, the format of the strstr() function is as follows: string strstr(string $haystack, mixed $needle) In the above syntax, the parameters involved are explained as follows haystack: specifies the character to be searched String, needle specifies the string to be searched. If the parameter is a number, it will match the character of the ASCII value of the number. In actual applications, there will be situations where the case of letters needs to be ignored. In this case, you can use PHP A case-insensitive search function is provided - the stristr() function. The use of this function is the same as the strstr() function.
2) Find the position of a string
strpos() function The function is similar to the strstr() function, except that it returns not a string, but the position where a string first appears in another string. The syntax format of strpos() is as follows: int strpos(string $haystack , mixed $needle[,int $offset =0]) The parameters involved in the above syntax are explained as follows: haystack is the string to be searched, needle specifies the string to be searched, and offset specifies the starting search. Position, the default value is 0.
The strpos() function is a case-sensitive search function, but in actual applications, it is often necessary to ignore case. In this case, you can use a case-sensitive search function provided by PHP Write a search function stripos() that is not very sensitive. The usage of this function is the same as strpos().

5, compare strings
In PHP language, comparing the size of two strings can be achieved in two ways: using the "==" operator comparison and using the function for comparison

1) using "= ="operator compares the size of two strings
When comparing two strings in PHP, the easiest way is to use the double equal sign operator (==).
2) Use functions to compare characters String size
The strcmp() function provided in PHP can more accurately compare the sizes of two strings. The syntax format is as follows int strcmp(string $str1, string $str2). The parameters involved in the above syntax are The description is as follows: str1 specifies the string 1 to be compared, str2 specifies the string 2 to be compared. This strcmp function can ensure whether the two strings completely match and return the comparison result in the form of an integer. The return of this function There are three types of values. 0: The two strings are equal. When it is less than 0, the first string is smaller than the following string. If the return value is greater than zero, then it means that the previous string is larger than the following string.
In addition to the strcmp() function, PHP also provides some other similar comparison functions. For example, the strncmp() function can select the length (number of characters) of the string you want to compare. ), the syntax format is as follows: int strcmp(string $str1, string $str2, int $len) The above parameter description str1: specifies the first string to be compared, str2: specifies the second string len to be compared. :Specify the number of characters used for comparison in each string.
When comparing strings, sometimes you need to ignore case, so you can use the strcasemp() function and strncasemp() function. These two functions are similar to The usage of the corresponding case-sensitive functions is exactly the same. The syntax formats of the strcasecmp() function and strncasecmp() are as follows:
int strcasecmp(string $str1,string $str2)
int strncasecmp (string $str1,string $str2,int $len)

6, copy string
If you need to repeat the function of displaying a character or a string n times, the simplest implementation method is to call Copy function. In PHP, you can use the str_repeat() function to copy strings. The syntax format of this function is as follows: string str_repeat(string $input, int $multiplier). The description of the parameters designed in the above syntax is as follows. The input specified For repeated strings, the multiplier specifies the number of times the string will be repeated.

7, Flip the string
The operation of processing the string also includes flipping the string. In the PHP language, use strrev() The function can realize the function of reversing a string. The syntax format of the strrev() function is
string strrev(string $string)
The above parameter string is used to specify the string to be reversed.

8, Split and merge strings
Split a string into multiple strings according to certain rules, or merge multiple strings into one long string, when processing string operations Problems that are often encountered. Use the explode() function, str_split() function, and implode() function provided by PHP to handle problems like splitting and merging strings.

1) Split strings
The function of the explode() function is to split the string into an array using the specified delimiter. The syntax format of the explode() function is as follows: array explode(string $delimiter, string $string[, int $limit]) in the above The parameters involved in the syntax are explained as follows: delimiter: specifies where to separate the string, string: specifies the string to be split, limit: specifies the maximum number of array elements returned, and the final sub-block will contain string. The remaining part.
The function of str_split() function is to split a string into multiple substrings of equal length. The syntax format of str_split() function is as follows: array str_split(string $string[,int $split_length=1 ]) The parameters in the above syntax are explained as follows: string: specifies the string to be split, split_length: specifies the length of each array element, the default value is "1".
2) Merge strings
implode( ) function is to connect the elements of the array into a string. The syntax format of the implode() function is as follows: string implode([string $glue], array $pieces). The parameters involved in the above syntax are described as follows: glue() specifies the content placed between array elements. The default value is "" (representing a space string) pieces specifies the array to be merged into a string. Calling the implode() function can obtain a new character according to the conditions restricted by the parameters. string to achieve the purpose of merging strings.
join() is an alias of the implode() function. The usage of the two functions is exactly the same. It needs to be emphasized that although the parameter glue is optional, in order to make the program For better compatibility, it is recommended to use two parameters.
Summarize the related operation methods of strings:

1) printf() function: You can format strings
2 )sprintf() function: You can format strings. The difference from printf() function is that you need to use echo to display and output the formatted string.
3)nl2br() function: You can format characters The newline character "\n" in the string is converted into "
" in HTML and displayed.
4)wordwrap() function: Specifies forced line wrapping from a certain column of characters
5)strtolower () function: The function implemented by this function is to convert all characters in the string into lowercase characters
6) strtoupper() function: The function of this function is to convert all the characters in the string to uppercase characters
7) ucwords() function: The function of this function is to convert all the first characters in the string Convert to uppercase characters
8) substr_replace() function: can quickly scan and edit strings with large text content
9) strlen() function: can calculate the length of a string and return the string The length
10)substr_count() function: can determine how many times a string is in the provided string
11)str_word_count() function, can determine the number of occurrences of a certain word in a string.
12) strstr() function, which can be used to find substrings. The return result of this function is all the content after the first occurrence of the substring
13) strpos() function, function and strstr() The function is similar, except that it returns not a string, but the position of the first occurrence of one string in another string.
14) strcmp() function, this function can accurately compare two The size of the string
15) The strncmp() function can select the length (number of characters) of the string to be compared
16) The strcasecmp() function can compare two characters while ignoring case Compare strings
17) The strncasecmp() function can compare the length or number of characters of two strings while ignoring case.
18) The str_repeat() function can be displayed repeatedly n times The function of a character or string
19) strrev() function, which provides the operation of flipping a string
20) The explode() function, which provides the function of dividing a string into multiple strings Function, specify the separator to split the string into an array.
21) The str_split() function can split a string into multiple substrings of equal length
22) The implode() function can divide the elements of the array into Connect them together to form a string
23) The join() function is used exactly the same as the implode() function. Its function is also to connect the array elements into a string

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