In PHP, the definition of a string can be in English single quotes ', or you can use double quotes in English.
But you must use the same single or double quotes to define strings, such as ' Hello World ' and ' Hello World ' for illegal string definitions.
What's the difference between single and double quotes?
PHP allows us to include string variables directly in a double quote string.
The contents of a single quote string are always considered normal characters, so the content in single quotes is not escaped more efficiently.
Copy Code code as follows:
$str = ' Hello ';
echo "STR is $STR"; Run Result: STR is hello
Echo ' str is $STR '; Run Result: STR is $STR
In PHP, variables in double quotes ($var) and special characters (such as \ r \ n) are escaped, and the content in single quotes is not escaped (so more efficient).
On the use of words,
I used to love to write this in a SQL string $sql = "SELECT * FROM table WHERE id = $id" so that the inside $id can be escaped, single quotes are not.
In short, see the actual situation to use, how convenient how to use.
The above is this article about the single double quotes in PHP analysis of the difference, I hope you can enjoy