I know this is an old question, but I think someone has to mention all pros & cons:
Better Syntax: That's personal preference.
Performance: No difference. As many mentioned, double-quote might be faster if using unrealistically many variables.
Better Usage: Single quote [mostly]. As @Khez said, with single quote you can concatenate anything, even function calls and variable modification, like so:
echo 'hi ' . trim[$name] . [$i + 1];. The only thing double-quote can do that single-quote cannot do is usage of \n, \r, \t and alike.
Readability: No difference [may personal preference apply].
Writability/Re-Writability/Debugging: In 1-line statements there is no difference, but when dealing with multiple lines, it's easier to comment/uncomment lines while debugging or writing. For example:
$q = 'SELECT ' .
't1.col1 ' .
',t2.col2 ' .
//',t3.col3 ' .
'FROM tbl1 AS t1 ' .
'LEFT JOIN tbl2 AS t2 ON t2.col2 = t1.col1 ' .
//'LEFT JOIN tbl3 AS t3 ON t3.col3 = t2.col2 ' .
'WHERE t1.col1 = ' . $x . ' ' .
' AND t2.col2 = ' . $y . ' ' .
//' AND t3.col3 = ' . $z . ' ' .
'ORDER BY t1.col1 ASC ' .
'LIMIT 10';
Less
Escaping: Single-quote. For single quote you need to escape 2 characters only [' and \]. For double quote you need to escape 2 characters [", \] and 3 more if required [$, { and }].
Less Changes: Single quote. For example if you have the following code:
echo 'Number ' . $i . '!';
And you need to increment 1 to $i, so it becomes likes:
echo 'Number ' . [$i + 1] . '!';
But for double quote, you will need to change this:
echo "Number $i!";
to this:
echo "Number " . [$i + 1] . "!";
Conclusion: Use what you prefer.
There are two string operators. The first is the concatenation operator ['.'], which returns the concatenation of its right and left arguments. The second is the concatenating assignment operator ['.='], which appends the argument on the right side to the argument on the left side. Please read Assignment Operators for more
information.
K.Alex ¶
9 years ago
As for me, curly braces serve good substitution for concatenation, and they are quicker to type and code looks cleaner. Remember to use double quotes [" "] as their content is parced by php, because in single quotes [' '] you'll get litaral name of variable provided:
anders dot benke at telia dot com ¶
18 years ago
A word of caution - the dot operator has the same precedence as + and -, which can yield unexpected results.
Example:
The above will print out "3" instead of "Result: 6", since first the string "Result3" is created and this is then added to 3 yielding 3, non-empty non-numeric strings being converted to 0.
To print "Result: 6", use parantheses to alter precedence:
Stephen Clay ¶
16 years ago
Use double quotes to concat more than two strings instead of multiple '.' operators. PHP is forced to re-concatenate with every '.' operator.
hexidecimalgadget at hotmail dot com ¶
13 years ago
If you attempt to add numbers with a concatenation operator, your result will be the result of those numbers as strings.
mariusads::at::helpedia.com ¶
14 years ago
Be careful so that you don't type "." instead of ";" at the end of a line.
It took me more than 30 minutes to debug a long script because of something like this:
The output is "axbc", because of the dot on the first line.
biziclop ¶
20 days ago
Some bitwise operators [the and, or, xor and not operators: & | ^ ~ ] also work with strings too since PHP4, so you don't have to loop through strings and do chr[ord[$s[i]]] like things.
See the documentation of the bitwise operators: //www.php.net/operators.bitwise
Live demo: //3v4l.org/MnFeb