การทดลองท 8_2 Editor Buffer Array Implementation

Transcription

1 การทดลองท 8_2 Editor Buffer Array Implementation * File: buffer.h * * This file defines the interface for the EditorBuffer class. #ifndef _buffer_h #define _buffer_h * Class: EditorBuffer * * This class represents an editor buffer, which maintains an ordered * sequence of characters along with an insertion point called the cursor. class EditorBuffer { public: * Constructor: EditorBuffer * Usage: EditorBuffer buffer; * * Creates an empty editor buffer. EditorBuffer(); * Destructor: ~EditorBuffer * Usage: (usually implicit) * * Frees any heap storage associated with this buffer. ~EditorBuffer(); * Methods: movecursorforward, movecursorbackward * Usage: buffer.movecursorforward(); * buffer.movecursorbackward(); * * These functions move the cursor forward or backward one character, * respectively. If the command would shift the cursor beyond either * end of the buffer, this method has no effect. void movecursorforward(); void movecursorbackward();

2 * Methods: movecursortostart, movecursortoend * Usage: buffer.movecursortostart(); * buffer.movecursortoend(); * * These functions move the cursor to the start or the end of this buffer. void movecursortostart(); void movecursortoend(); * Method: insertcharacter * Usage: buffer.insertcharacter(ch); * * Inserts the single character ch into this buffer at the cursor * position. The cursor is then advanced to follow the inserted * character, thereby allowing for consecutive insertions. void insertcharacter(char ch); * Method: deletecharacter * Usage: buffer.deletecharacter(); * * Deletes the character immediately after the cursor. If the cursor is * at the end of the buffer, the method has no effect. void deletecharacter(); * Method: showcontents * Usage: buffer.showcontents(); * * Displays the buffer contents on the console stream and notes the * position of the cursor. void showcontents(); #include "bufferpriv.h" ; #endif

3 * File: bufferpriv.h * * This file contains the private section of the EditorBuffer class for * the array-based editor. * Implementation notes: Buffer data structure * * In the array-based implementation of the buffer, the characters in the * buffer are stored in a dynamic array. In addition to the array, the * structure keeps track of the capacity of the buffer, the length of the * buffer, and the cursor position. The cursor position is the index of * the character that follows where the cursor would appear on the screen. private: Instance variables char *array; Dynamic array of characters int capacity; Allocated size of that array int length; Number of character in buffer int cursor; Index of character after cursor Make it illegal to copy editor buffers EditorBuffer(const EditorBuffer & value) { const EditorBuffer & operator=(const EditorBuffer & rhs) { return *this; Private method prototype void expandcapacity();

4 * File: ArrayBuffer.cpp * * This file implements the buffer.h interface using an array representation. #include <iostream> #include "buffer.h" using namespace std; Constants const int INITIAL_CAPACITY = 10; * Implementation notes: Constructor and destructor * * The constructor initializes the private fields. The destructor * frees the heap-allocated memory, which is the dynamic array. EditorBuffer::EditorBuffer() { capacity = INITIAL_CAPACITY; array = new char[capacity]; length = 0; cursor = 0; EditorBuffer::~EditorBuffer() { delete[] array; * Implementation notes: movecursor methods * * The four movecursor methods simply adjust the value of cursor. void EditorBuffer::moveCursorForward() { void EditorBuffer::moveCursorBackward() { void EditorBuffer::moveCursorToStart() { void EditorBuffer::moveCursorToEnd() {

5 * Implementation notes: insertcharacter and deletecharacter * * Each of the functions that inserts or deletes characters must shift * all subsequent characters in the array, either to make room for new * insertions or to close up space left by deletions. void EditorBuffer::insertCharacter(char ch) { void EditorBuffer::deleteCharacter() { * Implementation notes: showcontents * * This method prints the contents of the buffer with one space between * each character to leave room for a caret on the next line to indicate * the position of the cursor. void EditorBuffer::showContents() {

6 * Implementation notes: expandcapacity * * This private method doubles the capacity of the elements array whenever * it runs out of space. To do so, it must copy the pointer to the old * array, allocate a new array with twice the capacity, copy the characters * from the old array to the new one, and finally free the old storage. void EditorBuffer::expandCapacity() { char *oldarray = array; capacity *= 2; array = new char[capacity]; for (int i = 0; i < length; i++) { array[i] = oldarray[i]; delete[] oldarray;

7 * File: SimpleTextEditor.cpp * * This program implements a simple command-driven text editor, which is * used to test the EditorBuffer class. #include <iostream> #include <sstream> #include <cctype> #include "buffer.h" using namespace std; Function prototypes void executecommand(editorbuffer & buffer, string line); Main program int main() { EditorBuffer buffer; while (true) { string cmd; cout << "*"; getline(cin,cmd); if (cmd!= "") executecommand(buffer, cmd); buffer.showcontents(); return 0; * Function: executecommand * Usage: executecommand(buffer, line); * * Executes the command specified by line on the editor buffer. void executecommand(editorbuffer & buffer, string line) { switch (toupper(line[0])) { case 'I': for (int i = 1; i < line.length(); i++) { buffer.insertcharacter(line[i]); break; case 'D': buffer.deletecharacter(); break; case 'F': buffer.movecursorforward(); break; case 'B': buffer.movecursorbackward(); break; case 'J': buffer.movecursortostart(); break; case 'E': buffer.movecursortoend(); break; case 'Q': exit(0); default: cout << "Illegal command" << endl; break;