xpath: XML Path Language implementation

## xpath

xpath - XML Path Language implementation

API for the XML Path Language implementation XML Path Language implementation XPath is a language for addressing parts of an XML document, designed to be used by both XSLT and XPointer

Author(s): Daniel Veillard

## Synopsis

    #define XML_XPATH_CHECKNS;
    #define XML_XPATH_NOVAR;
    #define xmlXPathNodeSetGetLength(ns);
    #define xmlXPathNodeSetIsEmpty(ns);
    #define xmlXPathNodeSetItem(ns, index);
    typedef struct _xmlNodeSet xmlNodeSet;
    typedef xmlNodeSet * xmlNodeSetPtr;
    typedef struct _xmlXPathAxis xmlXPathAxis;
    typedef xmlXPathAxis * xmlXPathAxisPtr;
    typedef struct _xmlXPathCompExpr xmlXPathCompExpr;
    typedef xmlXPathCompExpr * xmlXPathCompExprPtr;
    typedef struct _xmlXPathContext xmlXPathContext;
    typedef xmlXPathContext * xmlXPathContextPtr;
    typedef enum xmlXPathError;
    typedef xmlXPathFunct * xmlXPathFuncPtr;
    typedef struct _xmlXPathFunct xmlXPathFunct;
    typedef struct _xmlXPathObject xmlXPathObject;
    typedef xmlXPathObject * xmlXPathObjectPtr;
    typedef enum xmlXPathObjectType;
    typedef struct _xmlXPathParserContext xmlXPathParserContext;
    typedef xmlXPathParserContext * xmlXPathParserContextPtr;
    typedef struct _xmlXPathType xmlXPathType;
    typedef xmlXPathType * xmlXPathTypePtr;
    typedef struct _xmlXPathVariable xmlXPathVariable;
    typedef xmlXPathVariable * xmlXPathVariablePtr;
    typedef xmlXPathObjectPtr xmlXPathAxisFunc	(xmlXPathParserContextPtr ctxt,
    						 xmlXPathObjectPtr cur);
    double	xmlXPathCastBooleanToNumber	(int val);
    xmlChar *	xmlXPathCastBooleanToString	(int val);
    int	xmlXPathCastNodeSetToBoolean	(xmlNodeSetPtr ns);
    double	xmlXPathCastNodeSetToNumber	(xmlNodeSetPtr ns);
    xmlChar *	xmlXPathCastNodeSetToString	(xmlNodeSetPtr ns);
    double	xmlXPathCastNodeToNumber	(xmlNodePtr node);
    xmlChar *	xmlXPathCastNodeToString	(xmlNodePtr node);
    int	xmlXPathCastNumberToBoolean	(double val);
    xmlChar *	xmlXPathCastNumberToString	(double val);
    int	xmlXPathCastStringToBoolean	(const xmlChar * val);
    double	xmlXPathCastStringToNumber	(const xmlChar * val);
    int	xmlXPathCastToBoolean		(xmlXPathObjectPtr val);
    double	xmlXPathCastToNumber		(xmlXPathObjectPtr val);
    xmlChar *	xmlXPathCastToString	(xmlXPathObjectPtr val);
    int	xmlXPathCmpNodes		(xmlNodePtr node1,
    					 xmlNodePtr node2);
    xmlXPathCompExprPtr	xmlXPathCompile	(const xmlChar * str);
    xmlXPathObjectPtr	xmlXPathCompiledEval	(xmlXPathCompExprPtr comp,
    						 xmlXPathContextPtr ctx);
    int	xmlXPathCompiledEvalToBoolean	(xmlXPathCompExprPtr comp,
    					 xmlXPathContextPtr ctxt);
    int	xmlXPathContextSetCache		(xmlXPathContextPtr ctxt,
    					 int active,
    					 int value,
    					 int options);
    xmlXPathObjectPtr	xmlXPathConvertBoolean	(xmlXPathObjectPtr val);
    typedef int xmlXPathConvertFunc		(xmlXPathObjectPtr obj,
    					 int type);
    xmlXPathObjectPtr	xmlXPathConvertNumber	(xmlXPathObjectPtr val);
    xmlXPathObjectPtr	xmlXPathConvertString	(xmlXPathObjectPtr val);
    xmlXPathCompExprPtr	xmlXPathCtxtCompile	(xmlXPathContextPtr ctxt,
    						 const xmlChar * str);
    xmlXPathObjectPtr	xmlXPathEval	(const xmlChar * str,
    					 xmlXPathContextPtr ctx);
    xmlXPathObjectPtr	xmlXPathEvalExpression	(const xmlChar * str,
    						 xmlXPathContextPtr ctxt);
    typedef void xmlXPathEvalFunc		(xmlXPathParserContextPtr ctxt,
    					 int nargs);
    int	xmlXPathEvalPredicate		(xmlXPathContextPtr ctxt,
    					 xmlXPathObjectPtr res);
    void	xmlXPathFreeCompExpr		(xmlXPathCompExprPtr comp);
    void	xmlXPathFreeContext		(xmlXPathContextPtr ctxt);
    void	xmlXPathFreeNodeSet		(xmlNodeSetPtr obj);
    void	xmlXPathFreeNodeSetList		(xmlXPathObjectPtr obj);
    void	xmlXPathFreeObject		(xmlXPathObjectPtr obj);
    typedef xmlXPathFunction xmlXPathFuncLookupFunc	(void * ctxt,
    						 const xmlChar * name,
    						 const xmlChar * ns_uri);
    typedef void xmlXPathFunction		(xmlXPathParserContextPtr ctxt,
    					 int nargs);
    void	xmlXPathInit			(void);
    int	xmlXPathIsInf			(double val);
    int	xmlXPathIsNaN			(double val);
    xmlXPathContextPtr	xmlXPathNewContext	(xmlDocPtr doc);
    xmlXPathObjectPtr	xmlXPathNodeEval	(xmlNodePtr node,
    						 const xmlChar * str,
    						 xmlXPathContextPtr ctx);
    xmlNodeSetPtr	xmlXPathNodeSetCreate	(xmlNodePtr val);
    xmlXPathObjectPtr	xmlXPathObjectCopy	(xmlXPathObjectPtr val);
    long	xmlXPathOrderDocElems		(xmlDocPtr doc);
    int	xmlXPathSetContextNode		(xmlNodePtr node,
    					 xmlXPathContextPtr ctx);
    void	xmlXPathSetErrorHandler		(xmlXPathContextPtr ctxt,
    					 xmlStructuredErrorFunc handler,
    					 void * data);
    typedef xmlXPathObjectPtr xmlXPathVariableLookupFunc	(void * ctxt,
    							 const xmlChar * name,
    							 const xmlChar * ns_uri);

## Description

## Details

### Macro XML_XPATH_CHECKNS

    #define XML_XPATH_CHECKNS;

check namespaces at compilation

### Macro XML_XPATH_NOVAR

    #define XML_XPATH_NOVAR;

forbid variables in expression

### Macro xmlXPathNodeSetGetLength

    #define xmlXPathNodeSetGetLength(ns);

Implement a functionality similar to the DOM NodeList.length. Returns the number of nodes in the node-set.

`ns`: | a node-set

### Macro xmlXPathNodeSetIsEmpty

    #define xmlXPathNodeSetIsEmpty(ns);

Checks whether @ns is empty or not. Returns %TRUE if @ns is an empty node-set.

`ns`: | a node-set

### Macro xmlXPathNodeSetItem

    #define xmlXPathNodeSetItem(ns, index);

Implements a functionality similar to the DOM NodeList.item(). Returns the xmlNodePtr at the given @index in @ns or NULL if @index is out of range (0 to length-1)

`ns`: | a node-set
`index`: | index of a node in the set

### Structure xmlNodeSet

    struct _xmlNodeSet {
        int	nodeNr	: number of nodes in the set
        int	nodeMax	: size of the array as allocated
        xmlNodePtr *	nodeTab	: array of nodes in no particular order @@ with_ns to check whether nam
    } xmlNodeSet;

### Typedef xmlNodeSetPtr

    xmlNodeSet * xmlNodeSetPtr;

### Structure xmlXPathAxis

    struct _xmlXPathAxis {
        const xmlChar *	name	: the axis name
        xmlXPathAxisFunc	func	: the search function
    } xmlXPathAxis;

### Typedef xmlXPathAxisPtr

    xmlXPathAxis * xmlXPathAxisPtr;

### Structure xmlXPathCompExpr

    struct _xmlXPathCompExpr {
    The content of this structure is not made public by the API.
    } xmlXPathCompExpr;

### Typedef xmlXPathCompExprPtr

    xmlXPathCompExpr * xmlXPathCompExprPtr;

### Structure xmlXPathContext

    struct _xmlXPathContext {
        xmlDocPtr	doc	: The current document
        xmlNodePtr	node	: The current node
        int	nb_variables_unused	: unused (hash table)
        int	max_variables_unused	: unused (hash table)
        xmlHashTablePtr	varHash	: Hash table of defined variables
        int	nb_types	: number of defined types
        int	max_types	: max number of types
        xmlXPathTypePtr	types	: Array of defined types
        int	nb_funcs_unused	: unused (hash table)
        int	max_funcs_unused	: unused (hash table)
        xmlHashTablePtr	funcHash	: Hash table of defined funcs
        int	nb_axis	: number of defined axis
        int	max_axis	: max number of axis
        xmlXPathAxisPtr	axis	: Array of defined axis the namespace nodes of the context node
        xmlNsPtr *	namespaces	: Array of namespaces
        int	nsNr	: number of namespace in scope
        void *	user	: function to free extra variables
        int	contextSize	: the context size
        int	proximityPosition	: the proximity position extra stuff for XPointer
        int	xptr	: is this an XPointer context?
        xmlNodePtr	here	: for here()
        xmlNodePtr	origin	: for origin() the set of namespace declarations in scope for the expre
        xmlHashTablePtr	nsHash	: The namespaces hash table
        xmlXPathVariableLookupFunc	varLookupFunc	: variable lookup func
        void *	varLookupData	: variable lookup data Possibility to link in an extra item
        void *	extra	: needed for XSLT The function name and URI when calling a function
        const xmlChar *	function
        const xmlChar *	functionURI	: function lookup function and data
        xmlXPathFuncLookupFunc	funcLookupFunc	: function lookup func
        void *	funcLookupData	: function lookup data temporary namespace lists kept for walking the n
        xmlNsPtr *	tmpNsList	: Array of namespaces
        int	tmpNsNr	: number of namespaces in scope error reporting mechanism
        void *	userData	: user specific data block
        xmlStructuredErrorFunc	error	: the callback in case of errors
        xmlError	lastError	: the last error
        xmlNodePtr	debugNode	: the source node XSLT dictionary
        xmlDictPtr	dict	: dictionary if any
        int	flags	: flags to control compilation Cache for reusal of XPath objects
        void *	cache	: Resource limits
        unsigned long	opLimit
        unsigned long	opCount
        int	depth
    } xmlXPathContext;

### Typedef xmlXPathContextPtr

    xmlXPathContext * xmlXPathContextPtr;

### Enum xmlXPathError

    enum xmlXPathError {
        XPATH_EXPRESSION_OK = 0
        XPATH_NUMBER_ERROR = 1
        XPATH_UNFINISHED_LITERAL_ERROR = 2
        XPATH_START_LITERAL_ERROR = 3
        XPATH_VARIABLE_REF_ERROR = 4
        XPATH_UNDEF_VARIABLE_ERROR = 5
        XPATH_INVALID_PREDICATE_ERROR = 6
        XPATH_EXPR_ERROR = 7
        XPATH_UNCLOSED_ERROR = 8
        XPATH_UNKNOWN_FUNC_ERROR = 9
        XPATH_INVALID_OPERAND = 10
        XPATH_INVALID_TYPE = 11
        XPATH_INVALID_ARITY = 12
        XPATH_INVALID_CTXT_SIZE = 13
        XPATH_INVALID_CTXT_POSITION = 14
        XPATH_MEMORY_ERROR = 15
        XPTR_SYNTAX_ERROR = 16
        XPTR_RESOURCE_ERROR = 17
        XPTR_SUB_RESOURCE_ERROR = 18
        XPATH_UNDEF_PREFIX_ERROR = 19
        XPATH_ENCODING_ERROR = 20
        XPATH_INVALID_CHAR_ERROR = 21
        XPATH_INVALID_CTXT = 22
        XPATH_STACK_ERROR = 23
        XPATH_FORBID_VARIABLE_ERROR = 24
        XPATH_OP_LIMIT_EXCEEDED = 25
        XPATH_RECURSION_LIMIT_EXCEEDED = 26
    };

### Typedef xmlXPathFuncPtr

    xmlXPathFunct * xmlXPathFuncPtr;

### Structure xmlXPathFunct

    struct _xmlXPathFunct {
        const xmlChar *	name	: the function name
        xmlXPathEvalFunc	func	: the evaluation function
    } xmlXPathFunct;

### Structure xmlXPathObject

    struct _xmlXPathObject {
        xmlXPathObjectType	type
        xmlNodeSetPtr	nodesetval
        int	boolval
        double	floatval
        xmlChar *	stringval
        void *	user
        int	index
        void *	user2
        int	index2
    } xmlXPathObject;

### Typedef xmlXPathObjectPtr

    xmlXPathObject * xmlXPathObjectPtr;

### Enum xmlXPathObjectType

    enum xmlXPathObjectType {
        XPATH_UNDEFINED = 0
        XPATH_NODESET = 1
        XPATH_BOOLEAN = 2
        XPATH_NUMBER = 3
        XPATH_STRING = 4
        XPATH_POINT = 5
        XPATH_RANGE = 6
        XPATH_LOCATIONSET = 7
        XPATH_USERS = 8
        XPATH_XSLT_TREE = 9 /*  An XSLT value tree, non modifiable */
    };

### Structure xmlXPathParserContext

    struct _xmlXPathParserContext {
        const xmlChar *	cur	: the current char being parsed
        const xmlChar *	base	: the full expression
        int	error	: error code
        xmlXPathContextPtr	context	: the evaluation context
        xmlXPathObjectPtr	value	: the current value
        int	valueNr	: number of values stacked
        int	valueMax	: max number of values stacked
        xmlXPathObjectPtr *	valueTab	: stack of values
        xmlXPathCompExprPtr	comp	: the precompiled expression
        int	xptr	: it this an XPointer expression
        xmlNodePtr	ancestor	: used for walking preceding axis
        int	valueFrame	: always zero for compatibility
    } xmlXPathParserContext;

### Typedef xmlXPathParserContextPtr

    xmlXPathParserContext * xmlXPathParserContextPtr;

### Structure xmlXPathType

    struct _xmlXPathType {
        const xmlChar *	name	: the type name
        xmlXPathConvertFunc	func	: the conversion function
    } xmlXPathType;

### Typedef xmlXPathTypePtr

    xmlXPathType * xmlXPathTypePtr;

### Structure xmlXPathVariable

    struct _xmlXPathVariable {
        const xmlChar *	name	: the variable name
        xmlXPathObjectPtr	value	: the value
    } xmlXPathVariable;

### Typedef xmlXPathVariablePtr

    xmlXPathVariable * xmlXPathVariablePtr;

### Function type xmlXPathAxisFunc

    xmlXPathObjectPtr	xmlXPathAxisFunc	(xmlXPathParserContextPtr ctxt,
    						 xmlXPathObjectPtr cur)

An axis traversal function. To traverse an axis, the engine calls the first time with cur == NULL and repeat until the function returns NULL indicating the end of the axis traversal.

`ctxt`: | the XPath interpreter context
`cur`: | the previous node being explored on that axis
`Returns`: | the next node in that axis or NULL if at the end of the axis.

### Function type xmlXPathConvertFunc

    int	xmlXPathConvertFunc		(xmlXPathObjectPtr obj,
    					 int type)

A conversion function is associated to a type and used to cast the new type to primitive values.

`obj`: | an XPath object
`type`: | the number of the target type
`Returns`: | -1 in case of error, 0 otherwise

### Function type xmlXPathEvalFunc

    void	xmlXPathEvalFunc		(xmlXPathParserContextPtr ctxt,
    					 int nargs)

An XPath evaluation function, the parameters are on the XPath context stack.

`ctxt`: | an XPath parser context
`nargs`: | the number of arguments passed to the function

### Function type xmlXPathFuncLookupFunc

    xmlXPathFunction	xmlXPathFuncLookupFunc	(void * ctxt,
    						 const xmlChar * name,
    						 const xmlChar * ns_uri)

Prototype for callbacks used to plug function lookup in the XPath engine.

`ctxt`: | an XPath context
`name`: | name of the function
`ns_uri`: | the namespace name hosting this function
`Returns`: | the XPath function or NULL if not found.

### Function type xmlXPathFunction

    void	xmlXPathFunction		(xmlXPathParserContextPtr ctxt,
    					 int nargs)

An XPath function. The arguments (if any) are popped out from the context stack and the result is pushed on the stack.

`ctxt`: | the XPath interprestation context
`nargs`: | the number of arguments

### Function type xmlXPathVariableLookupFunc

    xmlXPathObjectPtr	xmlXPathVariableLookupFunc	(void * ctxt,
    							 const xmlChar * name,
    							 const xmlChar * ns_uri)

Prototype for callbacks used to plug variable lookup in the XPath engine.

`ctxt`: | an XPath context
`name`: | name of the variable
`ns_uri`: | the namespace name hosting this variable
`Returns`: | the XPath object value or NULL if not found.

### Variable xmlXPathNAN

    double xmlXPathNAN;

### Variable xmlXPathNINF

    double xmlXPathNINF;

### Variable xmlXPathPINF

    double xmlXPathPINF;

### xmlXPathCastBooleanToNumber ()

    double	xmlXPathCastBooleanToNumber	(int val)

Converts a boolean to its number value

`val`: | a boolean
`Returns`: | the number value

### xmlXPathCastBooleanToString ()

    xmlChar *	xmlXPathCastBooleanToString	(int val)

Converts a boolean to its string value.

`val`: | a boolean
`Returns`: | a newly allocated string.

### xmlXPathCastNodeSetToBoolean ()

    int	xmlXPathCastNodeSetToBoolean	(xmlNodeSetPtr ns)

Converts a node-set to its boolean value

`ns`: | a node-set
`Returns`: | the boolean value

### xmlXPathCastNodeSetToNumber ()

    double	xmlXPathCastNodeSetToNumber	(xmlNodeSetPtr ns)

Converts a node-set to its number value

`ns`: | a node-set
`Returns`: | the number value

### xmlXPathCastNodeSetToString ()

    xmlChar *	xmlXPathCastNodeSetToString	(xmlNodeSetPtr ns)

Converts a node-set to its string value.

`ns`: | a node-set
`Returns`: | a newly allocated string.

### xmlXPathCastNodeToNumber ()

    double	xmlXPathCastNodeToNumber	(xmlNodePtr node)

Converts a node to its number value

`node`: | a node
`Returns`: | the number value

### xmlXPathCastNodeToString ()

    xmlChar *	xmlXPathCastNodeToString	(xmlNodePtr node)

Converts a node to its string value.

`node`: | a node
`Returns`: | a newly allocated string.

### xmlXPathCastNumberToBoolean ()

    int	xmlXPathCastNumberToBoolean	(double val)

Converts a number to its boolean value

`val`: | a number
`Returns`: | the boolean value

### xmlXPathCastNumberToString ()

    xmlChar *	xmlXPathCastNumberToString	(double val)

Converts a number to its string value.

`val`: | a number
`Returns`: | a newly allocated string.

### xmlXPathCastStringToBoolean ()

    int	xmlXPathCastStringToBoolean	(const xmlChar * val)

Converts a string to its boolean value

`val`: | a string
`Returns`: | the boolean value

### xmlXPathCastStringToNumber ()

    double	xmlXPathCastStringToNumber	(const xmlChar * val)

Converts a string to its number value

`val`: | a string
`Returns`: | the number value

### xmlXPathCastToBoolean ()

    int	xmlXPathCastToBoolean		(xmlXPathObjectPtr val)

Converts an XPath object to its boolean value

`val`: | an XPath object
`Returns`: | the boolean value

### xmlXPathCastToNumber ()

    double	xmlXPathCastToNumber		(xmlXPathObjectPtr val)

Converts an XPath object to its number value

`val`: | an XPath object
`Returns`: | the number value

### xmlXPathCastToString ()

    xmlChar *	xmlXPathCastToString	(xmlXPathObjectPtr val)

Converts an existing object to its string() equivalent

`val`: | an XPath object
`Returns`: | the allocated string value of the object, NULL in case of error. It's up to the caller to free the string memory with xmlFree().

### xmlXPathCmpNodes ()

    int	xmlXPathCmpNodes		(xmlNodePtr node1,
    					 xmlNodePtr node2)

Compare two nodes w.r.t document order

`node1`: | the first node
`node2`: | the second node
`Returns`: | -2 in case of error 1 if first point < second point, 0 if it's the same node, -1 otherwise

### xmlXPathCompile ()

    xmlXPathCompExprPtr	xmlXPathCompile	(const xmlChar * str)

Compile an XPath expression

`str`: | the XPath expression
`Returns`: | the xmlXPathCompExprPtr resulting from the compilation or NULL. the caller has to free the object.

### xmlXPathCompiledEval ()

    xmlXPathObjectPtr	xmlXPathCompiledEval	(xmlXPathCompExprPtr comp,
    						 xmlXPathContextPtr ctx)

Evaluate the Precompiled XPath expression in the given context.

`comp`: | the compiled XPath expression
`ctx`: | the XPath context
`Returns`: | the xmlXPathObjectPtr resulting from the evaluation or NULL. the caller has to free the object.

### xmlXPathCompiledEvalToBoolean ()

    int	xmlXPathCompiledEvalToBoolean	(xmlXPathCompExprPtr comp,
    					 xmlXPathContextPtr ctxt)

Applies the XPath boolean() function on the result of the given compiled expression.

`comp`: | the compiled XPath expression
`ctxt`: | the XPath context
`Returns`: | 1 if the expression evaluated to true, 0 if to false and -1 in API and internal errors.

### xmlXPathContextSetCache ()

    int	xmlXPathContextSetCache		(xmlXPathContextPtr ctxt,
    					 int active,
    					 int value,
    					 int options)

Creates/frees an object cache on the XPath context. If activates XPath objects (xmlXPathObject) will be cached internally to be reused. @options: 0: This will set the XPath object caching: @value: This will set the maximum number of XPath objects to be cached per slot There are two slots for node-set and misc objects. Use <0 for the default number (100). Other values for @options have currently no effect.

`ctxt`: | the XPath context
`active`: | enables/disables (creates/frees) the cache
`value`: | a value with semantics dependent on @options
`options`: | options (currently only the value 0 is used)
`Returns`: | 0 if the setting succeeded, and -1 on API or internal errors.

### xmlXPathConvertBoolean ()

    xmlXPathObjectPtr	xmlXPathConvertBoolean	(xmlXPathObjectPtr val)

Converts an existing object to its boolean() equivalent

`val`: | an XPath object
`Returns`: | the new object, the old one is freed (or the operation is done directly on @val)

### xmlXPathConvertNumber ()

    xmlXPathObjectPtr	xmlXPathConvertNumber	(xmlXPathObjectPtr val)

Converts an existing object to its number() equivalent

`val`: | an XPath object
`Returns`: | the new object, the old one is freed (or the operation is done directly on @val)

### xmlXPathConvertString ()

    xmlXPathObjectPtr	xmlXPathConvertString	(xmlXPathObjectPtr val)

Converts an existing object to its string() equivalent

`val`: | an XPath object
`Returns`: | the new object, the old one is freed (or the operation is done directly on @val)

### xmlXPathCtxtCompile ()

    xmlXPathCompExprPtr	xmlXPathCtxtCompile	(xmlXPathContextPtr ctxt,
    						 const xmlChar * str)

Compile an XPath expression

`ctxt`: | an XPath context
`str`: | the XPath expression
`Returns`: | the xmlXPathCompExprPtr resulting from the compilation or NULL. the caller has to free the object.

### xmlXPathEval ()

    xmlXPathObjectPtr	xmlXPathEval	(const xmlChar * str,
    					 xmlXPathContextPtr ctx)

Evaluate the XPath Location Path in the given context.

`str`: | the XPath expression
`ctx`: | the XPath context
`Returns`: | the xmlXPathObjectPtr resulting from the evaluation or NULL. the caller has to free the object.

### xmlXPathEvalExpression ()

    xmlXPathObjectPtr	xmlXPathEvalExpression	(const xmlChar * str,
    						 xmlXPathContextPtr ctxt)

Alias for xmlXPathEval().

`str`: | the XPath expression
`ctxt`: | the XPath context
`Returns`: | the xmlXPathObjectPtr resulting from the evaluation or NULL. the caller has to free the object.

### xmlXPathEvalPredicate ()

    int	xmlXPathEvalPredicate		(xmlXPathContextPtr ctxt,
    					 xmlXPathObjectPtr res)

Evaluate a predicate result for the current node. A PredicateExpr is evaluated by evaluating the Expr and converting the result to a boolean. If the result is a number, the result will be converted to true if the number is equal to the position of the context node in the context node list (as returned by the position function) and will be converted to false otherwise; if the result is not a number, then the result will be converted as if by a call to the boolean function.

`ctxt`: | the XPath context
`res`: | the Predicate Expression evaluation result
`Returns`: | 1 if predicate is true, 0 otherwise

### xmlXPathFreeCompExpr ()

    void	xmlXPathFreeCompExpr		(xmlXPathCompExprPtr comp)

Free up the memory allocated by @comp

`comp`: | an XPATH comp

### xmlXPathFreeContext ()

    void	xmlXPathFreeContext		(xmlXPathContextPtr ctxt)

Free up an xmlXPathContext

`ctxt`: | the context to free

### xmlXPathFreeNodeSet ()

    void	xmlXPathFreeNodeSet		(xmlNodeSetPtr obj)

Free the NodeSet compound (not the actual nodes !).

`obj`: | the xmlNodeSetPtr to free

### xmlXPathFreeNodeSetList ()

    void	xmlXPathFreeNodeSetList		(xmlXPathObjectPtr obj)

Free up the xmlXPathObjectPtr @obj but don't deallocate the objects in the list contrary to xmlXPathFreeObject().

`obj`: | an existing NodeSetList object

### xmlXPathFreeObject ()

    void	xmlXPathFreeObject		(xmlXPathObjectPtr obj)

Free up an xmlXPathObjectPtr object.

`obj`: | the object to free

### xmlXPathInit ()

    void	xmlXPathInit			(void)

DEPRECATED: Alias for xmlInitParser.

### xmlXPathIsInf ()

    int	xmlXPathIsInf			(double val)

Checks whether a double is an infinity.

`val`: | a double value
`Returns`: | 1 if the value is +Infinite, -1 if -Infinite, 0 otherwise

### xmlXPathIsNaN ()

    int	xmlXPathIsNaN			(double val)

Checks whether a double is a NaN.

`val`: | a double value
`Returns`: | 1 if the value is a NaN, 0 otherwise

### xmlXPathNewContext ()

    xmlXPathContextPtr	xmlXPathNewContext	(xmlDocPtr doc)

Create a new xmlXPathContext

`doc`: | the XML document
`Returns`: | the xmlXPathContext just allocated. The caller will need to free it.

### xmlXPathNodeEval ()

    xmlXPathObjectPtr	xmlXPathNodeEval	(xmlNodePtr node,
    						 const xmlChar * str,
    						 xmlXPathContextPtr ctx)

Evaluate the XPath Location Path in the given context. The node 'node' is set as the context node. The context node is not restored.

`node`: | the node to to use as the context node
`str`: | the XPath expression
`ctx`: | the XPath context
`Returns`: | the xmlXPathObjectPtr resulting from the evaluation or NULL. the caller has to free the object.

### xmlXPathNodeSetCreate ()

    xmlNodeSetPtr	xmlXPathNodeSetCreate	(xmlNodePtr val)

Create a new xmlNodeSetPtr of type double and of value @val

`val`: | an initial xmlNodePtr, or NULL
`Returns`: | the newly created object.

### xmlXPathObjectCopy ()

    xmlXPathObjectPtr	xmlXPathObjectCopy	(xmlXPathObjectPtr val)

allocate a new copy of a given object

`val`: | the original object
`Returns`: | the newly created object.

### xmlXPathOrderDocElems ()

    long	xmlXPathOrderDocElems		(xmlDocPtr doc)

Call this routine to speed up XPath computation on static documents. This stamps all the element nodes with the document order Like for line information, the order is kept in the element->content field, the value stored is actually - the node number (starting at -1) to be able to differentiate from line numbers.

`doc`: | an input document
`Returns`: | the number of elements found in the document or -1 in case of error.

### xmlXPathSetContextNode ()

    int	xmlXPathSetContextNode		(xmlNodePtr node,
    					 xmlXPathContextPtr ctx)

Sets 'node' as the context node. The node must be in the same document as that associated with the context.

`node`: | the node to to use as the context node
`ctx`: | the XPath context
`Returns`: | -1 in case of error or 0 if successful

### xmlXPathSetErrorHandler ()

    void	xmlXPathSetErrorHandler		(xmlXPathContextPtr ctxt,
    					 xmlStructuredErrorFunc handler,
    					 void * data)

Register a callback function that will be called on errors and warnings. If handler is NULL, the error handler will be deactivated. Available since 2.13.0.

`ctxt`: | the XPath context
`handler`: | error handler
`data`: | user data which will be passed to the handler