User Guide

44 Chapter 3: Using ColdFusion Variables
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 Chapter 1, “Reserved
Words and Variables” in 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” on page 70.
For more information on how to create variables, see “Creating and using variables in scopes”
on page 67.
Variable naming rules
ColdFusion 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” on page 56.
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, you should 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” on page 64.