PHP String Handling Functions

Key Points

• PHP provides a large number of built-in string processing functions that can manipulate strings in various ways. These functions include changing the case of a string, finding the length of a string, replacing part of the string, and so on. Key functions include strlen(), str_replace(), strpos(), strtolower(), strtoupper(), substr(), and
.
• trim() The ltrim() function in PHP can remove spaces at the beginning and end of a string or other specified characters, which helps to clean up user input before processing. The rtrim() and
functions perform similar operations, but only remove characters on the left or right side of the string, respectively.
• substr() The strpos() function in PHP is used to intercept strings and can specify where to start intercepting and how long it is intercepted. Use this in conjunction with the str_replace() function to extract text from a string accurately. The
function allows replacing specific words or characters in a string.

PHP has a large number of built-in string handling functions that allow you to easily manipulate strings in almost any way possible. However, it can be a bit daunting to learn all of these functions, remembering their functions and the time when they may come in handy, especially for novice developers. It is impossible to cover every string function in one article, and the PHP manual exists for this! But I'll show how to use some common string handling functions you should know. After learning, you will be able to manipulate strings as skillfully as any performer!

Case conversion

strtoupper()PHP provides functions that enable you to manipulate the case of characters in strings without editing strings character by character. Why do you care about this? Maybe you want to make sure that some text is capitalized in all, such as acronyms, titles, to emphasize or just to make sure that the name is capitalized correctly. Or, you might just want to compare two strings, and you want to make sure the letters you are comparing are the same character set. The case conversion function is easy to master; you just need to pass the string as a parameter to the function, and the return value is the processed string. If you want to make sure all letters in a specific string are capitalized, you can use the

function as shown below:

<?php
$str = "Like a puppet on a string.";
$cased = strtoupper($str);
// 显示：LIKE A PUPPET ON A STRING.
echo $cased;
?>

strtolower()It may be obvious, but it is still worth noting that numbers and other non-alphabetical characters are not converted. As you might guess, the strtoupper() function does exactly the opposite of

, which converts a string to all lowercase letters:

<?php
$str = "LIKE A PUPPET ON A STRING.";
$cased = strtolower($str);
// 显示：like a puppet on a string.
echo $cased;
?>

ucwords()At other times, you may want to make sure that certain words (such as names or titles) only capitalize the first letter of each word. For this purpose, you can use the

function:

<?php
$str = "Like a puppet on a string.";
$cased = strtoupper($str);
// 显示：LIKE A PUPPET ON A STRING.
echo $cased;
?>

You can also use the lcfirst() and ucfirst() functions to manipulate the case of the first letter of a string. If you want to lowercase the first letter, use lcfirst(). If you want to capitalize the first letter, use ucfirst(). The ucfirst() function is probably the most useful because you can use it to make sure that sentences always start with capital letters.

<?php
$str = "LIKE A PUPPET ON A STRING.";
$cased = strtolower($str);
// 显示：like a puppet on a string.
echo $cased;
?>

Quick trim

Sometimes it is necessary to trim the edges of the string. It may have spaces or other characters at the beginning or end that need to be removed. Spaces can be actual space characters, or tab characters, carriage return characters, etc. An example of a situation where you might need to do this is when you process user input and want to clean it up before starting processing. The trim() function in PHP allows you to do this; you can pass a string as a parameter and will delete all spaces at the beginning and end of the string:

<?php
$str = "a knot";
$cased = ucwords($str);
// 显示：A Knot
echo $cased;
?>

trim() is also versatile, in addition to strings, you can pass a set of characters that will remove any characters that match it at the beginning or end:

<?php
$str = "how long is a piece of string?";
$cased = ucfirst($str);
// 显示：How long is a piece of string?
echo $cased;
?>

Be careful when using these additional characters, because trim() The space will be removed only if you explicitly provide one of the characters you want to delete as a space:

<?php
$str = "  A piece of string?  ";
// 显示：string(22) " A piece of string? "
var_dump($str);

$trimmed = trim($str);
// 显示：string(18) "A piece of string?"
var_dump($trimmed);
?>

Even if trim() only deletes characters at the beginning and end of the string, it also deletes "A" and spaces because when "A" is deleted, the spaces become the new beginning of the string and are therefore deleted. There are also ltrim() and rtrim() functions in PHP, which are similar to trim() functions, but only delete spaces (or other specified characters) on the left or right side of the string, respectively.

String length

You often need to know its length when processing a string. For example, when working on a form, you might have a field that you want to make sure that the user cannot exceed a certain number of characters. To calculate the number of characters in a string, use the strlen() function:

<?php
$str = "A piece of string?";
$trimmed = trim($str, "A?");
// 显示：string(16) " piece of string"
var_dump($trimmed);
?>

Intercept the string

Another common situation is to look up a specific text in a given string and "cut" it out so that you can do other operations on it. To cut a string to a specified size, you need a good pair of scissors, in PHP, your scissors are the substr() function. To use the substr() function, pass the string to be processed as a parameter, as well as a positive or negative integer. This number determines where you will start cutting the string; 0 starts with the first character of the string (remember, when you iterate through the string, the first character on the left starts at position 0, not 1).

<?php
$str = "A piece of string?";
$trimmed = trim($str, "A ?");
// 显示：string(15) "piece of string"
var_dump($trimmed);
?>

When using a negative number, substr() will start backward from the end of the string.

<?php
$str = "How long is a piece of string?";
$size = strlen($str);
// 显示：30
echo $size;
?>

The optional third parameter for

substr() is length, another integer value, which allows you to specify the number of characters to be extracted from the string.

<?php
$str = "Like a puppet on a string.";
$cased = strtoupper($str);
// 显示：LIKE A PUPPET ON A STRING.
echo $cased;
?>

If you only need to find the location of the specific text in the string without any other operation, you can use the strpos() function, which returns the position of your choice relative to the beginning of the string. A useful trick, especially if you don't know the starting position of the text you want to cut from a string, is to use these two functions together. Instead of specifying the start position as an integer, you can search for a specific text and then extract that text.

<?php
$str = "LIKE A PUPPET ON A STRING.";
$cased = strtolower($str);
// 显示：like a puppet on a string.
echo $cased;
?>

Replace

Finally, let's see how to replace part of a string with something else, for which the str_replace() function can be used. This is great for cases where you just want to replace instances of a specific word or a set of characters in a string and replace it with something else:

<?php
$str = "a knot";
$cased = ucwords($str);
// 显示：A Knot
echo $cased;
?>

If you want to replace multiple values, you can also provide an array for str_replace():

<?php
$str = "how long is a piece of string?";
$cased = ucfirst($str);
// 显示：How long is a piece of string?
echo $cased;
?>

str_replace() is case sensitive, so if you don't want to worry about this, you can use its case-insensitive sibling function str_ireplace().

Summary

I hope this article has given you some of the operations of using strings in PHP and makes you eager to learn more. I actually just touched on the fur! The best way to understand all the different string functions is to spend some time reading the String Functions page in the PHP manual. I'd love to know which string functions you use most often, so feel free to mention them in the comments below. Pictures from Vasilius / Shutterstock

Frequently Asked Questions for PHP String Processing Functions

What are some common PHP string processing functions and their uses?

PHP provides a wide range of string processing functions. Some of the most commonly used functions include:

1. strlen(): This function returns the length of the string.
2. str_replace(): This function replaces certain characters with other characters in the string.
3. strpos(): This function finds where the string first appears in another string.
4. strtolower(): This function converts a string to lowercase.
5. strtoupper(): This function converts a string to uppercase.
6. substr(): This function returns part of the string.

These functions are used to manipulate and process strings in various ways, such as changing the case of a string, finding the length of a string, replacing part of the string, and so on.

How to convert a string to an array in PHP?

In PHP, the str_split() function is used to convert strings into arrays. This function splits the string into an array by length. Here is an example:

<?php
$str = "  A piece of string?  ";
// 显示：string(22) " A piece of string? "
var_dump($str);

$trimmed = trim($str);
// 显示：string(18) "A piece of string?"
var_dump($trimmed);
?>

In this example, the str_split() function splits the string "Hello, World!" into an array where each element is a single character in the string.

How to compare two strings in PHP?

PHP provides several functions for comparing strings, including strcmp(), strcasecmp(), strnatcmp(), and strnatcasecmp(). The strcmp() function performs binary-safe and case-sensitive comparisons of two strings. Here is an example:

<?php
$str = "Like a puppet on a string.";
$cased = strtoupper($str);
// 显示：LIKE A PUPPET ON A STRING.
echo $cased;
?>

In this example, the strcmp() function compares the strings "Hello" and "World". If string1 is greater than string2, the function returns 0, and if they are equal, 0.

How to reverse a string in PHP?

The strrev() function in PHP is used to invert strings. Here is an example:

<?php
$str = "LIKE A PUPPET ON A STRING.";
$cased = strtolower($str);
// 显示：like a puppet on a string.
echo $cased;
?>

In this example, the strrev() function inverts the string "Hello, World!".

How to remove spaces from PHP strings?

The trim() function in PHP is used to remove spaces and other predefined characters from both sides of a string. Here is an example:

<?php
$str = "a knot";
$cased = ucwords($str);
// 显示：A Knot
echo $cased;
?>

In this example, the trim() function deletes the spaces at the beginning and end of the string "Hello, World!".

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