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Creating variables
You
create most ColdFusion variables by assigning them values. (You
must use the ArrayNew function to create
arrays.) Most commonly, you create variables by using the cfset tag. You can also use
the cfparam tag, and assignment statements
in CFScript. Tags that create data objects also create variables.
For example, the cfquery tag creates a query
object variable.
ColdFusion automatically creates some variables that provide
information about the results of certain tags or operations. ColdFusion
also automatically generates variables in certain scopes, such as
Client and Server. For information on these special variables, see Reserved
Words and Variables in the CFML Reference and the
documentation of the CFML tags that create these variables.
ColdFusion generates an error when it tries to use a variable
before it is created. This can happen, for example, when processing
data from an incompletely filled form. To prevent such errors, test
for the variable’s existence before you use it. For more information
on testing for variable existence, see Ensuring variable existence.
For more information on how to create variables, see Creating and using variables in scopes.
Variable naming rulesColdFusion variable names, including form
field names and custom function and ColdFusion component argument
names, must conform to Java naming rules and the following guidelines:
A variable name must begin with a letter, underscore,
or Unicode currency symbol.
The initial character can by followed by any number of letters,
numbers, underscore characters, and Unicode currency symbols.
A variable name cannot contain spaces.
A query result is a type of variable, so it overwrites a
local variable with the same name.
ColdFusion variables are not case sensitive. However, consistent
capitalization makes the code easier to read.
When creating a form with fields that are used in a query,
match form field names with the corresponding database field names.
Periods separate the components of structure or object names.
They also separate a variable scope from the variable name. You
cannot use periods in simple variable names, with the exception
of variables in the Cookie and Client scopes. For more information
on using periods, see Using periods in variable references.
The following rule applies to variable names, but does not apply
to form field and argument names:
Prefix each variable’s name with its scope. Although
some ColdFusion programmers do not use the Variables prefix for
local variable names, use prefixes for all other scopes. Using scope
prefixes makes variable names clearer and increases code efficiency.
In many cases, you must prefix the scope. For more information,
see About scopes.
Note: In some cases, when you use
an existing variable name, you must enclose it with number signs
(#) to allow ColdFusion to distinguish it from string or HTML text,
and to insert its value, as opposed to its name. For more information,
see Using number signs.
Variable characteristicsYou can classify a variable using the following characteristics:
The data type of the variable value, which indicates
the kind of information a variable represents, such as number, string,
or date
The scope of the variable, which indicates where the information
is available and how long the variable persists.
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