Single quotes or double quotes for variable concatenation? [closed]

Question

Is it better to concatenate a variable (say, $name) into an existing string (say, $string) like this:

$string='Hi, my name is '.$name 

or to embed the variable in the string like this:

$string="Hi, my name is $name"; 

or is it better to use a function like this:

$string=sprintf("Hi, my name is %s",$name); 

Which is better in terms of processor time/efficiency?

Answer 1

Everyone who did the test concluded that using single quotes is marginally better performance wise. In the end single quotes result in just a concatenation while double quotes forces the interpreter to parse the complete string for variables.

However the added load in doing that is so small for the last versions of PHP that most of the time the conclusion is that it doesn't really matter.

So for the performance people: use single quotes. For the "i like my code readable"-people: double quotes are a lot better for the legibility, as Flavius Stef already pointed out.

Edit: One thing though - If you are going to use a a single dollar in your string without a variable, use single quotes for sure! (http://www.weberdev.com/get_example-3750.html points out that it will take 4 times longer to parse those strings)

Answer 2

The difference between single and double quotes in PHP is that double quotes are "intelligent" in that they will parse for variables when being read, while single quotes are "dumb" and will not try to parse any character in the string.

These result in some minor differences in what characters you can use; basically, the only character you need to escape when using single quotes is a single quote itself:

'\'' 

While if you use double quotes you have to escape other characters:

"\$" 

But it also allows for some nifty things like adding a new-line to the end:

"my string\n" 

With single quotes you would have to do a concatenation:

'my string' . chr(10) 'my string' . "\n" 

Generally, single quotes are faster because they are "dumb".

However, normally one should not really worry about these issues, that is called Premature optimization, and should be avoided.

A couple of words about optimization: generally one should first write the program the way it should work, and then find the biggest bottlenecks and fix those particular ones. If string speed really is an issue for you in PHP, you might want to consider switching to another language.

Regarding speed: you probably want to focus more on memory usage than on CPU time. In these cases the CPU time could be considered pretty constant. CPU time is more relevant when writing algorithms that will iterate many times.

Regarding concatenations: the more you concatenate strings using the dot-operator, the more memory you will be using.

Consider this:

$str1 = 'asdf'; $str2 = 'qwer';  // this will result in more memory being allocated for temporary storage echo $str1 . $str2;  // this will not allocate as much memory as the previous example echo $str1; echo $str2;