Teach you how to use string functions to insert backslashes before characters

Today we will introduce a new chapter, string functions. String functions are part of the PHP core and no installation is required to use these functions. Today we will introduce it.

Old rules, first let’s talk about what a string function is.

String functions, also known as string processing functions, refer to functions used for string processing in programming languages, such as string copying, length calculation, character search, etc., which can be used in C, Functions used in Pascal, visual and LotusScript.

After we understand what string functions are, let's start today's topic, inserting a backslash before the character.

In fact, there are two ways to insert a backslash before a character. There is a little difference between the two methods. Let's look at the first one first.

The first, addcslashes() function

Let’s look at a small example first.

<?php
$str = addcslashes("Hello World!","W");
echo($str);
?>

The result is

Hello \World!

As can be seen from this example, we add "\" in front of "w", and this w is also specified externally, So the addcslashes() function can insert a backslash before the specified character.

Let’s see if that’s right, yes it is. The addcslashes() function returns a string with a backslash added before the specified character.

It should be noted that the addcslashes() function is case sensitive. Be careful when applying addcslashes() to 0 (NULL), r (carriage return), n (line feed), t (form feed), f (tab), and v (vertical tab). In PHP, \0, \r, \n, \t, \f and \v are predefined escape sequences.

Now that the first method has been introduced, let’s take a look at the second method to see what the difference is between this method and the previous one.

Second type, addslashes() function

Let’s look at a small example.

<?php
$str = addslashes(&#39;What does "yolo" mean?&#39;);
echo($str);
?>

The result is

What does \"yolo\" mean?

This example is different from the previous example. It does not specify characters, but adds a backslash in front of some characters. It is so magical. What's going on? We take a closer look at the code and find that there is a double quote after the backslash. Is this the reason? Let's take a look at the answer.

addslashes() function returns a string with a backslash added before predefined characters, and this function can be used to prepare appropriate strings for strings stored in the database and database query statements.

The predefined characters are:

• Single quotation mark (')

• Double quotation mark (")

• Backslash (\)

• NULL

magic_quotes_gpc is on, automatically runs addslashes() for all GET, POST and COOKIE data. Do not Use addslashes() for strings that have been escaped by magic_quotes_gpc, because this will cause double-level escaping. When encountering this situation, you can use the function get_magic_quotes_gpc() for detection.

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