面试题与答案

The output is displayed directly to the browser.

In this example it wouldn't matter, since the variable is all by itself, but if you were to print something like "{$a},000,000 mln dollars", then you definitely need to use the braces.

Via define() directive, like define ("MYCONSTANT", 100);

Just like in C++, put an ampersand in front of it, like $a = &$b

When the original if was followed by : and then the code block without braces.

Expression preceding the ? is evaluated, if it's true, then the expression preceding the : is executed, otherwise, the expression following : is executed.
E.g $id = isset($_GET['id']) ? $_GET['id'] : false;

parent::constructor($value)

Because inside the single quotes the n character is not interpreted as newline, just as a sequence of two characters - and n.

Since the data inside the single-quoted string is not parsed for variable substitution, it's always a better idea speed-wise to initialize a string with single quotes, unless you specifically need variable substitution.

The first one is octal 23, the second is hex 23.

 $var1 = 'Welcome to '; $var2 = 'TechInterviews.com';

What will work faster? Code sample 1: -

$var 3 = $var1.$var2;

Or code sample 2:

$var3 = "$var1$var2";

Both examples would provide the same result - $var3 equal to "Welcome to TechInterviews.com". However, Code Sample 1 will work significantly faster. Try it out with large sets of data (or via concatenating small sets a million times or so), and you will see that concatenation works significantly faster than variable substitution.