Read XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition Online
Authors: Michael Kay
XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (527 page)
The detailed rules for establishing the effective boolean value may appear somewhat arbitrary. They were defined this way in large measure for backward compatibility with XPath 1.0, which allowed sequences of nodes but did not allow sequences of strings, booleans, or numbers. The rules will probably come naturally if you are familiar with weakly typed languages such as Perl or Python, but there are a few traps to beware of. For example, if you convert the boolean value
false
to a string, you get the string
“false”
, but the effective boolean value of this string is
true
.
The
boolean()
function does not always return the same result as the
xs:boolean()
constructor.
xs:boolean()
(like
cast
as
xs:boolean
) follows the rules in XML Schema that define the lexical representations of the
xs:boolean
type. This treats the strings
“1”
and
“true”
as
true
, and
“0”
and
“false”
as
false
; anything else is an error.
XSLT Examples
The following example prints a message if the source document contains a
, or if it contains a
and no
or neither
The conversion of the two node sequences//header(true if there are any//footer(true if there are any
elements) needs to be explicit here, because we want to do a boolean comparison, not a comparison of two node sequences.
The following example sets a variable to the
xs:boolean
value
true
or
false
, depending on whether the document contains footnotes. In this case the explicit conversion is probably not necessary, since it could be done later when the variable is used, but it is probably more efficient to retain only an
xs:boolean
value in the variable rather than retaining the full set of footnote nodes. An intelligent XSLT processor will recognize that the expression//footnoteoccurs in a context where a boolean is required, and scan the document only until the first footnote is found, rather than retrieving all of them. (In this example, however, using the function
exists()
would achieve the same effect.)
See Also
exists()
on page 778
false()
on page 779
true()
on page 899
ceiling
The
ceiling()
function rounds a supplied number up to the nearest whole number. For example, the expressionceiling(33.9)returns
34
.
Changes in 2.0
The function has been generalized to work on all numeric types.
Signature
| Argument | Type | Meaning |
| value | Numeric | The supplied value. |
| Result | Numeric | The result of rounding $value up to the next highest integer. The result has the same primitive type as the supplied value . |
Effect
If the number is an
xs:integer
, or is equal to an
xs:integer
, then it is returned unchanged.
Otherwise, it is rounded up to the next highest whole number. If the supplied value is an
xs:decimal
, the result will be an
xs:decimal
, if it is an
xs:double
, the result will be an
xs:double
, and if it is an
xs:float
, the result will be an
xs:float
.
The
xs:double
and
xs:float
types in XPath support special values such as infinity, negative zero and NaN (not-a-number), which are described on page 199 in Chapter 5. If the argument is NaN, the result will be NaN. Similarly, when the argument is positive or negative infinity, the function will return the value of the argument unchanged.
