DBFile Class Reference

#include <DBFile.h>

List of all members.

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Detailed Description

Low level database file.

This abstraction allows the user to treat a database as a collection of pages.

Author:

Dave Musicant, with considerable material reused from the UW-Madison Minibase project

Public Member Functions
	DBFile (string name, int numPages)
	Creates a database with the specified number of pages.
	DBFile (string name)
	Opens the database with the given name.
int	allocatePages (int runSize)
	Allocates a set of pages.
void	deallocatePages (int startPageNum, int runSize)
	Deallocates a set of pages.
void	readPage (int pageNum, Page *page)
	Reads the contents of the specified page from disk into the page object provided.
void	writePage (int pageNum, const Page *page)
	Writes the contents of the specified page to disk.
Static Public Member Functions
static bool	erase (string name)
	Erases the database entirely from the filesystem.

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Constructor & Destructor Documentation

DBFile::DBFile	(	string	name,
		int	numPages
	)

Creates a database with the specified number of pages.

The number of pages in the database can never be increased.

Parameters:

	name	name to be given to database.
	numPages	maximum number of pages in database.

Exceptions:

IOException

if problem with file system.

DBFile::DBFile

(

string

name

)

Opens the database with the given name.

Parameters:

name

name of the database.

Exceptions:

IOException

if problem with file system.

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Member Function Documentation

int DBFile::allocatePages

(

int

runSize

)

Allocates a set of pages.

Parameters:

runSize

number of pages to be allocated in the run.

Returns:

page number of the first page of the allocated run.

Exceptions:

	NonPositiveRunSizeException	if the run size is less than or equal to zero.
	FileFullException	if there are not enough free pages.

void DBFile::deallocatePages	(	int	startPageNum,
		int	runSize
	)

Deallocates a set of pages.

Does not ensure that the pages being deallocated are in fact allocated to begin with. If the pages were already deallocated, they remain so.

Parameters:

	startPageNum	page number at the beginning of the run to be deallocated.
	runSize	number of pages to deallocate.

Exceptions:

	NonPositiveRunSizeException	if the run size is less than or equal to zero.
	BadPageNumberException	if startPageNum is illegal.

static bool DBFile::erase

(

string

name

)

[static]

Erases the database entirely from the filesystem.

Dangerous to do if still have a DBFile object that refers to this file.

Parameters:

name

name of the database.

Returns:

true if operation succeeded.

void DBFile::readPage	(	int	pageNum,
		Page *	page
	)

Reads the contents of the specified page from disk into the page object provided.

Parameters:

	pageNum	the page number to be read.
	page	a pointer to an already allocated Page object.

Exceptions:

BadPageNumberException

if pageNum is not in the file.

void DBFile::writePage	(	int	pageNum,
		const Page *	page
	)

Writes the contents of the specified page to disk.

Parameters:

	pageNum	the page number to be written.
	page	a pointer to a Page object with data to be written.

Exceptions:

	EmptyFileException()	if the file has no pages within it.
	BadPageNumberException	if pageNum is not in the file.

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