Whats the difference between these codes [closed] - php

Question

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Closed 9 years ago.
I am a beginner in PHP and trying to learn and want to know the difference between these codes:
echo "<div>$lang[CATEGORY_NAME]</div>";
echo "<div>" . $lang['CATEGORY_NAME'] . "</div>";
and when I should use each one.

Answer 1

Ill split my answer into 3 parts.
1. Double quotes string
In other words code like
echo "foo lol";
In double quotes string the PHP interpreter look for variables inside the string, and replaces them with their value. So the following code
$lol = "how are you";
echo "foo $lol";
will produce the following output.
foo how are you
Note that in double quoted string, the PHP interpreter will always look for variable and will replace them with their value, even if there are no variables in the string (this can cause performance issue, but later on this).
2. Single quoted string
i.e. code like
$lol = 'hello';
echo '$lol user';
In this case, PHP interpreter outputs the string as is. So if you did not guess yet, the output will be
$lol user
(see the $lol was not replaced by its value, in this case $lol is just a string that start with the dollar sign (not a variable).
3. String concatenation
As the name implied, used to concatenate string. The special PHP character . (dot) used to concatenate strings, for example
$lol = 'hello';
$bar = 'user';
echo $lol . ' ' . $bar . '. How are you?';
And the output will be
hello user. How are you?
Performance and usage
Now to the answer. As I said already, double quoted string will look for variables in them, so if you do not plan to output variable inside string, its always faster to use single quoted strings.
As for outputting variables, its always better to concatenate them with single quoted string as opposed to use double quoted strings.
See the following example:
echo "Hello {$arr['var1']['var2']}. How are you?";
This code is unclear, and it might cause problems when you want to output string that contains quotes in them and etc. Also as you noted (thanks for Martina comment), if you want to output arrays with keys, you have to surround them with { and }, so variable inside double quoted strings are a mess to read.
This code
echo 'Hello ' . $arr['var1']['var2'] . '. How are you?';
Is more readable, and faster in parsing.
Hope this answers your question :)

Answer 2

echo '<div>' . $lang['CATEGORY_NAME'] . '</div>';
This has the advantage of not searching for variables inside quotes (use single quotes otherwise parser has to check for variables in the string).

Answer 3

The variable inside double comma string is variable. So when the code is parsed it is treated as variable. In the later example you are concatinating the string with $variable. the later method should be used because it gives clear readness and take less time to parse the code.
Another thing is that you can use single commas for the later example and double commas for first example. But separating $variables from string and using concat is a good practice.
Single Comma with variable
Example :
echo '<div>$lang[CATEGORY_NAME]</div>';
Output
<div>$lang[CATEGORY_NAME]</div>
Single Comma with concat
echo '<div>' . $lang['CATEGORY_NAME'] . '</div>';
Output
Category_name // whatever
Double Comma with variable
Example :
echo "<div>$lang[CATEGORY_NAME]</div>";//parser will search for variable inside string
Output
Category_name // whatever
Double Comma with concat
echo "<div>" . $lang['CATEGORY_NAME'] . "</div>";
Output
Category_name // whatever
Now it's up to you what you want to choose.

Answer 4

When PHP meets double quotes ", it performs a string scanning to evaluate any variable that may have been mentioned inside (at runtime), that needs to be evaluated. Unlike ", single quotes ' make PHP use the string as is, without further evaluation and is therefore faster.
In this case,
echo '<div>' . $lang['CATEGORY_NAME'] . '</div>';
is slightly better as the <div> and </div> tags won't need any more evaluation from PHP. Additionally, PHP can perform some optimization with $lang['CATEGORY_NAME'] as it flags what it is at compilation time (thanks to APC, compilation is done only once after the script file changes).
In the first case
echo "<div>$lang[CATEGORY_NAME]</div>";
the string is parsed at runtime, and is therefore slightly more expensive than the above version.