The trim() function of PHP can be used to remove whitespace characters or other specified characters at the beginning and end of a string. 1. By default, trim() removes spaces, tabs (\t), line breaks (\n), carriage return (\r), empty bytes (\0), and vertical tabs (\x0B); for example, trim(" \n\tHello World!\r\n ") outputs Hello World!. 2. You can specify the characters to be removed through the second parameter, such as trim("---Hello World!---", "-") to return Hello World!, and support multiple characters, such as trim("xxxyour-string-yyyx", "xy") to get your-string. 3. Notes include: character-by-character checking rather than overall matching, no need to escape ordinary characters, and no affecting multi-byte characters. 4. Common applications include: cleaning form input, processing CSV data, analyzing log files and cleaning before string splicing.

Sometimes when we process strings, we will encounter unwanted characters before and after, such as spaces, line breaks or other symbols. At this time, PHP's trim() function will be used to "cut out" these unnecessary content.

trim() is most commonly used to remove whitespace characters at the beginning and end of a string, but it actually supports removing other characters you specify.

How to use trim to remove default whitespace characters

PHP's trim() function will remove the following blank class characters by default:

• Spaces
• Tab characters ( \t )
• Line breaks ( \n )
• Carriage return character ( \r )
• Null bytes ( \0 )
• Vertical tab character ( \x0B )

For example:

 $str = " \n\tHello World!\r\n ";
echo trim($str);

The output is:

 Hello World!

This usage is very common, especially when processing user input, such as data read from a form or file, which may have many invisible blanks before and after, and it will be much cleaner after processing with trim() .

How to customize the characters to be removed

If you not only want to remove whitespace characters, but also want to delete some specific characters, such as quotes, commas or other symbols, you can specify them in the second parameter of trim() .

The syntax is like this:

 trim(string $string, string $character_mask): string

For example:

 $str = "--Hello World!---";
echo trim($str, "-");

The result is:

 Hello World!

Note: trim() starts deleting from both sides until it encounters the first character not in $character_mask , and will not remove the middle ones.

You can pass multiple characters in, for example:

 trim("xxxyour-string-yyyx", "xy");

This will remove the x and y at the beginning and end, and the result will become "your-string" .

Notes and FAQs

There are several small details that are easily overlooked when using trim() :

• The characters in the second parameter are "checked one by one" and do not match the entire string together.
• If you accidentally write trim($str, "abc") , it will remove a, b, or c, instead of just removing the combination "abc".
• Don't forget to escape special characters. For example, if you want to remove the slash / , just write it in directly, but if you use regular expression-related functions, you should pay attention to the difference.
• It has no effect on multi-byte characters such as Chinese, it is just a character at the byte level.

Give an example that is not right:

 trim("abbaTestabb", "ab");
// The result is "Test"

Because the first two abs are removed, the ending abs are also removed.

Practical application suggestions

• Form submission data cleaning: trim($_POST['username']) can prevent users from accidentally entering the front and back spaces.
• When processing CSV file contents, fields may have some weird symbols, and you can use trim($field, "\"' ") to remove quotes and spaces.
• In log analysis, invalid characters on the head and tail of each line of log are cleaned.
• String pre-stitching to avoid the appearance of unnecessary connection symbols.

Basically that's it. Although it is simple, it can save a lot of trouble if it is used well in the project.

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