PHP Developer''''s Dictionary- P20 pptx
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PHP Developer’s Dictionary
IT-SC book
95
Table 4.5. Truth Table for the
and
Operator
variable1
variable2
Result
False
False
False
False
True
False
True
False
False
True
True
True
or
Syntax
variable1 or variable2
Description
The
or
operator evaluates whether either variable1 or variable2 is true. Table 4.6
contains the truth table for the possible values. In understanding the truth table, you
can see the only time the equation returns false is when both variable1 and
variable2
are false.
Note
The only difference between this operator and the
||
operator is order
precedence.
Table 4.6. Truth Table for the
or
Operator
variable1
variable2
Result
False
False
False
False
True
True
True
False
True
True
True
True
xor
Syntax
variable1 xor variable2
PHP Developer’s Dictionary
IT-SC book
96
Description
The xor, or exclusive or operator, evaluates whether either variable1 and
variable2 , but not both, is true. Table 4.7
contains the truth table for the possible
values. In understanding the truth table, you can see when variable1 and
variable2 are the same, false is returned.
Table 4.7. Truth Table for the
xor
Operator
variable1
variable2
Result
False
False
False
False
True
True
True
False
True
True
True
False
! (not)
Syntax
!variable
Description
The
!
, or not operator, returns the opposite of variable
. For instance, if variable
is true, applying the
!
operator will return false.
&& (and)
Syntax
variable1 && variable2
Description
The
&&
operator evaluates whether variable1 and variable2 are true, or equal.
Table 4.8
contains the truth table for the possible values. In understanding the truth
table, you can see the only time the equation returns true is when both variable1
and variable2 are true.
Note
The only difference between this operator and the
and
operator is order
precedence.
PHP Developer’s Dictionary
IT-SC book
97
Table 4.8. Truth Table for
&&
Operator
variable1
variable2
Result
False
False
False
False
True
False
True
False
False
True
True
True
|| (or)
Syntax
variable1 || variable2
Description
The
||
operator evaluates whether either variable1 or variable2 is true. Table 4.9
contains the truth table for the possible values. In understanding the truth table, you
can see the only time the equation returns false is when both variable1 and
variable2
are false.
Note
The only difference between this operator and the
or
operator is order
precedence.
Table 4.9. Truth Table for the
||
Operator
variable1
variable2
Result
False
False
False
False
True
True
True
False
True
True
True
True
String
The string operators are used to perform manipulation on the string data types.
Although some of the previous operators discussed in this section can be performed
on strings as well, these are limited to strings only.
. (Concatenation)
PHP Developer’s Dictionary
IT-SC book
98
Syntax
string1 . string2
Description
The
.
, or concatenation operator, will "add" string2
to string1
when applied. For
instance, if string1 ="P"
and string2 ="HP"
,
string1 . string2
would equal
"PHP"
.
$string1 = "hel";
$string2 = "p";
$string3 = "lo";
$result1 = $sting1 . $string2; // $result1 has "help"
$result2 = $sting1 . $string3; // $result2 has "hello"
.= (Concatenating Assignment)
Syntax
string1 .= string2
Description
The
.
, or concatenating assignment operator, will "add" string2
to string1
when
applied and then store the new string in string1 . For instance, if string1 ="P"
and
string2 ="HP"
, then
string1 .= string2
would equal
"PHP"
and that would be the
new value of string1
.
Predefined Variables
Predefined variables in PHP refer to language elements that are consistent across all
applications run in that environment. This is very much like the environment
variables you see within the UNIX and Windows operating systems. (Type
env
at a
command line to see a list of your operating system variables.)
Apache
The Apache predefined variables reflect the environment settings of your Apache
Web server when running PHP. There are also variables that reflect information
about a request of a given user-agent, or browser. This enables you to grab the
requested URL, query string, or another element of the HTTP request.
PHP Developer’s Dictionary
IT-SC book
99
DOCUMENT_ROOT
Syntax
string DOCUMENT_ROOT
Description
The
DOCUMENT_ROOT
variable contains the document root, as defined in the PHP
configuration file, under which the current script is being parsed.
GATEWAY_INTERFACE
Syntax
string GATEWAY_INTERFACE
Description
The
GATEWAY_INTERFACE
variable contains the version of the Common Gateway
Interface (CGI) specification that the server is using. For instance,
CGI/1.1
is a valid
GATEWAY_INTERFACE.
HTTP_ACCEPT
Syntax
string HTTP_ACCEPT
Description
The
HTTP_ACCEPT
variable contains the contents of the HTTP
Accept:
header if the
user-agent sent it to the server.
HTTP_ACCEPT_CHARSET
Syntax
string HTTP_ACCEPT_CHARSET
