InputBuffer.hpp

#ifndef INC_InputBuffer_hpp__
#define INC_InputBuffer_hpp__
 
/* ANTLR Translator Generator
 * Project led by Terence Parr at http://www.jGuru.com
 * Software rights: http://www.antlr.org/license.html
 *
 * $Id$
 */
 
#include <antlr/config.hpp>
#include <antlr/CircularQueue.hpp>
#include <string>
 
#ifdef ANTLR_CXX_SUPPORTS_NAMESPACE
namespace antlr {
#endif
 
/** A Stream of characters fed to the lexer from a InputStream that can
 * be rewound via mark()/rewind() methods.
 * <p>
 * A dynamic array is used to buffer up all the input characters.  Normally,
 * "k" characters are stored in the buffer.  More characters may be stored during
 * guess mode (testing syntactic predicate), or when LT(i>k) is referenced.
 * Consumption of characters is deferred.  In other words, reading the next
 * character is not done by conume(), but deferred until needed by LA or LT.
 * <p>
 *
 * @see antlr.CharQueue
 */
class ANTLR_API InputBuffer {
public:
        /** Create a character buffer */
        InputBuffer()
        : nMarkers(0)
        , markerOffset(0)
        , numToConsume(0)
        {
        }
 
        virtual ~InputBuffer()
        {
        }
 
        /// Reset the input buffer to empty state
        virtual inline void reset( void )
        {
                nMarkers = 0;
                markerOffset = 0;
                numToConsume = 0;
                queue.clear();
        }
 
        /** This method updates the state of the input buffer so that
         * the text matched since the most recent mark() is no longer
         * held by the buffer.  So, you either do a mark/rewind for
         * failed predicate or mark/commit to keep on parsing without
         * rewinding the input.
         */
        inline void commit( void )
        {
                nMarkers--;
        }
 
        /** Mark another character for deferred consumption */
        virtual inline void consume()
        {
                numToConsume++;
        }
 
        /** Ensure that the character buffer is sufficiently full */
        virtual void fill(unsigned int amount);
 
        /** Override this in subclasses to get the next character */
        virtual int getChar()=0;
 
        /** Get a lookahead character */
        virtual inline int LA(unsigned int i)
        {
                fill(i);
                return queue.elementAt(markerOffset + i - 1);
        }
 
        /** Return an integer marker that can be used to rewind the buffer to
         * its current state.
         */
        virtual unsigned int mark();
        /// Are there any marks active in the InputBuffer
        virtual inline bool isMarked() const
        {
                return (nMarkers != 0);
        }
        /** Rewind the character buffer to a marker.
         * @param mark Marker returned previously from mark()
         */
        virtual void rewind(unsigned int mark);
 
        /** Get the number of non-consumed characters
         */
        virtual unsigned int entries() const;
 
        ANTLR_USE_NAMESPACE(std)string getLAChars() const;
 
        ANTLR_USE_NAMESPACE(std)string getMarkedChars() const;
 
protected:
        // char source
        // leave to subclasses
 
        // Number of active markers
        unsigned int nMarkers; // = 0;
 
        // Additional offset used when markers are active
        unsigned int markerOffset; // = 0;
 
        // Number of calls to consume() since last LA() or LT() call
        unsigned int numToConsume; // = 0;
 
        // Circular queue
        CircularQueue<int> queue;
 
        /** Sync up deferred consumption */
        void syncConsume();
 
private:
        InputBuffer(const InputBuffer& other);
        InputBuffer& operator=(const InputBuffer& other);
};
 
/** Sync up deferred consumption */
inline void InputBuffer::syncConsume() {
        if (numToConsume > 0)
        {
                if (nMarkers > 0)
                        markerOffset += numToConsume;
                else
                        queue.removeItems( numToConsume );
                numToConsume = 0;
        }
}
 
#ifdef ANTLR_CXX_SUPPORTS_NAMESPACE
}
#endif
 
#endif //INC_InputBuffer_hpp__