The substr_replace() function in PHP language replaces a substring of a specified length.

The substr_replace() function in the PHP language is a very practical string processing function, which can be used to replace a substring of a specified length.

The syntax of the substr_replace() function is as follows:

substr_replace($string, $replacement, $start [, $length]);

Among them, $string represents the original string to be replaced, $replacement represents the replaced string, and $start represents the starting position of the replacement. Index, $length represents the length of the replaced string. If the $length parameter is omitted, it defaults to the end of the string.

Let’s look at a practical example below:

$str = 'Hello, world!';
$newStr = substr_replace($str, 'PHP', 7, 5);

echo $newStr; // Hello, PHP!

In the above example, we replace the substring of length 5 starting from the 7th position in the original string $str into the string 'PHP', and save the replacement result in the $newStr variable.

In addition to replacing a substring of a specified length, the substr_replace() function can also be used to insert a new substring into a string. We just need to set the $length parameter to 0 to achieve this.

The following is an example of inserting a substring:

$str = 'Hello, world!';
$newStr = substr_replace($str, 'my!', 6, 0);

echo $newStr; // Hello, my! world!

In the above example, we replace the 0 characters starting from the 6th position in the original string $str with the substring String 'my!', thus achieving the purpose of inserting a new substring into the string.

It should be noted that the substr_replace() function returns a new string instead of modifying the original string. If we need to modify the original string, we need to reassign the new string to the original string.

Finally, it should be pointed out that the substr_replace() function is only a way to replace strings in the PHP language. There are many other string processing functions that can also achieve similar functions. Therefore, when processing strings, we need to choose the appropriate function to use according to specific needs.

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