boolean()

Description

boolean() converts its argument to a boolean value following the XPath 1.0 type-conversion rules. The result is always true or false.

The conversion rules depend on the type of the argument:

• Node-set: true if the node-set is non-empty, false otherwise.
• String: true if the string has a length greater than zero, false for the empty string "".
• Number: true if the number is not zero and not NaN, false for 0 and NaN.
• Boolean: returned unchanged.

In practice, most XPath predicates and xsl:if/@test expressions perform an implicit boolean conversion, so an explicit call to boolean() is needed only when you want to convert a value to a boolean for output or further processing.

Parameters

Return value

xs:boolean — true or false according to the XPath 1.0 boolean conversion rules.

Examples

Convert a string to boolean

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<config>
  <label>active</label>
  <empty></empty>
</config>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/config">
    <results>
      <has-label><xsl:value-of select="boolean(label)"/></has-label>
      <has-empty><xsl:value-of select="boolean(empty)"/></has-empty>
    </results>
  </xsl:template>
</xsl:stylesheet>

Output:

<results>
  <has-label>true</has-label>
  <has-empty>false</has-empty>
</results>

Convert a number to boolean

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<data>
  <count>5</count>
  <zero>0</zero>
</data>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/data">
    <results>
      <count-bool><xsl:value-of select="boolean(number(count))"/></count-bool>
      <zero-bool><xsl:value-of select="boolean(number(zero))"/></zero-bool>
    </results>
  </xsl:template>
</xsl:stylesheet>

Output:

<results>
  <count-bool>true</count-bool>
  <zero-bool>false</zero-bool>
</results>

Notes

• An empty node-set, an empty string, the number 0, and NaN all convert to false. Everything else converts to true.
• Calling boolean() explicitly is uncommon inside xsl:if/@test because XPath already evaluates the test expression as a boolean. Use it when you need to output the literal string "true" or "false".
• NaN (produced by operations like number('abc')) converts to false, not an error.
• In XSLT 2.0+ the xs:boolean() constructor and the fn:boolean() function behave similarly but operate on sequences; an empty sequence returns false.

See also

• not()
• true()
• false()