A string is a continuous sequence of characters, consisting of numbers, letters and symbols. Each character in the string takes up only one byte.
In PHP, there are three ways to define strings, namely single quotes ('), double quotes (") and delimiters (
Single quotes and double quotes are often used to define strings. They are defined as follows:
Single quotes
<?php
$a='PHP中文网';
?>
Copy after login
Double quotes
<?php
$a="PHP中文网";
?>
Copy after login
The difference between single quotes and double quotes is that the variables contained in double quotes will be automatically replaced with actual values, while the variables contained in single quotes will be output as ordinary characters. What should I change in this paragraph? What does it mean? Let’s take a look at an example
An example of the difference between single quotes and double quotes defining strings
In this example, we use single quotes and double quotes to output the same variable, but the output results are completely different , as can be seen from the above figure, the result we use double quotes to output is the value of the variable, while the result we use single quotes to output is the string "$i"
In addition to the above differences, again. There is a difference in the use of transfer characters between the two. When using single quotes, you only need to transfer the single quotes " ' ", but when using double quotes ("), you must also pay attention to " " ", " $ " and other characters. For use, these special characters must be displayed through the escape character "\". Commonly used escape characters are as follows:
Commonly used escape characters
Escape characters
Input Output
\n
Newline
\r
Enter
\t
Horizontal tab
\\
Backslash
##\$
Dollar sign
\'
Single quotes
\"
Double quotes
##\[0-7]{1,3}
Regular expression matches a character represented by octal notation
\x[0-9A-Fa-f]{1,2}
Regular expression The formula matches a character represented by hexadecimal notation
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这里有一点要注意的是，\n和\r在Windows系统中没有什么区别，都可以当作回车符。但是在Linux系统中则是两种效果，在Linux中，\n表示换到下一行，却不会回到行首；而\r表示光标回到行首，但仍然在本行，如果有使用Linux操作系统的，可以尝试一下。
结束标识符必须单独另起一行，并且不允许有空格。在标识符前后有其他字符或符号，也会发生系统错误，包括注释。
