PHP中引号的使用之间的区别[重复]

Question

Possible Duplicate:
Difference between single quote and double quote string in php

Can you use " and ' interchangeably, 100%? Or is there a reason or use for each? What is the difference exactly?

Answer 1

Observe for yourself:

$name = 'John';
echo "Hello $name" . '<br>';
echo 'Hello $name';

Result:

Hello John   // result from double quotes
Hello $name  // result from single quotes

As can be seen variables inside double quotes are parsed while in single quotes they aren't.

So when you put variables inside double quotes, they can be parsed and their correct value is output whereas with single quotes, variables are not parsed and you get the same output of variable name itself as in Hello $name.

Since variables inside single quotes aren't parsed, using them is just a little good when it comes to performance.

If there is no question of variables inside quotes, you can use them inter-changeably though keeping above performance tip in mind.

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For more information, you can look at the official documentation.