Programming PHP

Table 2-2. Escape sequences in double-quoted strings (continued)
Escape sequence Character represented
\r Carriage return
\t Tab
\\ Backslash
\$ Dollar sign
\{ Left brace
\} Right brace
\[ Left bracket
\] Right bracket
\0 through \777 ASCII character represented by octal value
\x0 through \xFF ASCII character represented by hex value
A single-quoted string only recognizes \\ to get a literal backslash and \' to get a literal
single quote:
$dos_path = 'C:\\WINDOWS\\SYSTEM';
$publisher = 'Tim O\'Reilly';
echo "$dos_path $publisher\n";
C:\WINDOWS\SYSTEM Tim O'Reilly
To test whether two strings are equal, use the == comparison operator:
if ($a == $b) { echo "a and b are equal" }
Use the is_string( ) function to test whether a value is a string:
if (is_string($x)) {
// $x is a string
}
PHP provides operators and functions to compare, disassemble, assemble, search,
replace, and trim strings, as well as a host of specialized string functions for working
with HTTP, HTML, and SQL encodings. Because there are so many string-manipulation
functions, we’ve devoted a whole chapter (Chapter 4) to covering all the details.
Booleans
A boolean value represents a “truth value”—it says whether something is true or not.
Like most programming languages, PHP defines some values as true and others as
false. Truth and falseness determine the outcome of conditional code such as:
if ($alive) { ... }
In PHP, the following values are false:
• The keyword false
• The integer 0
• The floating-point value 0.0
26 | Chapter 2: Language Basics
This is the Title of the Book, eMatter Edition
Copyright © 2002 O’Reilly & Associates, Inc. All rights reserved.