Although the expression evaluation mechanism in ColdFusion is very powerful, it cannot automatically convert all data. For example, the expression "eight" * 10 produces an error because ColdFusion cannot convert the string "eight" to the number 8. Therefore, you must understand the rules for conversion between data types.

The following table explains how conversions are performed. The first column shows values to convert. The remaining columns show the result of conversion to the listed data type.

ColdFusion cannot convert complex types, such as arrays, queries, and COM objects, to other types. However, it can convert simple data elements of complex types to other simple data types.

Type conversion considerations

The following sections detail specific rules and considerations for converting between types.

The cfoutput tag

The cfoutput tag always displays data as a string. As a result, when you display a variable using the cfoutput tag, ColdFusion applies the type conversion rules to any non-string data before displaying it. For example, the cfoutput tag displays a date-time value as an ODBC timestamp.

Case-insensitivity and Boolean conversion

Because ColdFusion expression evaluation is not case-sensitive, Yes, YES, and yes are equivalent; False, FALSE, and false are equivalent; No, NO, and no are equivalent; and True, TRUE, and true are equivalent.

Converting binary data

ColdFusion cannot automatically convert binary data to other data types. To convert binary data, use the ToBase64 and ToString functions. For more information, see Binary data type and binary encoding.

Converting date and time data

To ensure that a date and time value is expressed as a real number, add zero to the variable. The following example shows this:

<cfset mynow = now()>
Use cfoutput to display the result of the now function:<br>
<cfoutput>#mynow#</cfoutput><br>
Now add 0 to the result and display it again:<br>
<cfset mynow = mynow + 0>
<cfoutput>#mynow#</cfoutput>

At 1:06 PM on June 6, 2003, its output looked like this:

Use cfoutput to display the result of the now function:
{ts '2003-06-03 13:06:44'}
Now add 0 to the result and display it again:
37775.5463426 

Converting numeric values

When ColdFusion evaluates an expression that includes both integers and real numbers, the result is a real number. To convert a real number to an integer, use a ColdFusion function. The Int, Round, Fix, and Ceiling functions convert real numbers to integers, and differ in their treatment of the fractional part of the number.

If you use a hidden form field with a name that has the suffix _integer or _range to validate a form input field, ColdFusion truncates real numbers entered into the field and passes the resulting integer to the action page.

If you use a hidden form field with a name that has the suffix _integer, _float, or _range to validate a form input field, and the entered data contains a dollar amount (including a dollar sign) or a numeric value with commas, ColdFusion considers the input to be valid, removes the dollar sign or commas from the value, and passes the resulting integer or real number to the action page.

ColdFusion does not have an inherent data type for arbitrary precision decimal numbers (BigDecimal numbers). ColdFusion initially saves such numbers as strings, and if you use them in an expression, converts the value to a numeric type, often losing precision. You can retain precision by using the PrecisionEvaluate method, which evaluates string expressions using BigDecimal precision arithmetic and can return the result as a long string of numbers. For more information, see PrecisionEvaluate in the CFML Reference.