StoredColumns Class Reference

#include <StoredColumns.hpp>

Public Member Functions
	StoredColumns ()
	StoredColumns (string filename)
	~StoredColumns ()
void	close ()
const vector< string > &	columnNames () const
const vector< string > &	columnUnits () const
const double *	nextRow ()
void	open (string filepath)

Private Attributes
vector< string >	_columnNames
vector< string >	_columnUnits
const double *	_endRow
string	_filePath
const double *	_nextRow
size_t	_numColumns

Detailed Description

An instance of the StoredColumns class provides access to a set of data columns stored in a file using the binary SKIRT stored columns format (which is simular to the SKIRT stored table format implemented by StoredTable). Stored columns files are intended as a much faster replacement for large regular text column data files, without the benefit of being human readable. The format does not support non-leaf rows, so it cannot be used for representing adaptive mesh data.

Stored columns file format

A stored columns file includes the names and units of the quantities in each column, in addition to the tabulated data values. All values are stored as binary data in the form of 64-bit floating-point numbers. More specifically, a stored columns file is essentially a sequence of 8-byte data items. A data item can have one of three types:

- string: 1 to 8 printable and non-whitespace 7-bit ASCII characters, padded with spaces
  to fill 8 bytes if needed;
- unsigned integer: 64-bit integer in little-endian byte order;
- floating point: 64-bit double (IEEE 754) in little-endian byte order.

The overall layout is as follows:

• SKIRT name/version tag
• Endianness tag
• 0 (to differentiate from stored table format, which stores the nr of axes here)
• numRows
• numColumns
• columnName (x numColumns)
• columnUnit (x numColumns)
• value (x numColumns x numRows)
• end-of-file tag

The values are ordered so that the column values for a particular row are next to each other.

The StoredColumns class

The default constructor creates an invalid stored columns instance. The alternate constructor and the open() function associate a particular stored columns file with the stored columns instance. The close() function and the destructor automatically release the file association and any related resources. It is allowed to call open() again after close().

The columnNames() and columnUnits() functions return informaton about the columns, and the readRow() function returns the rows one by one, from the start to the end of the file.

Constructor & Destructor Documentation

StoredColumns() [1/2]

StoredColumns::StoredColumns ( )

inline

The default constructor constructs a closed stored columns instance. The user must call the open() function to associate the instance with a particular stored columns file.

StoredColumns() [2/2]

StoredColumns::StoredColumns ( string  filename )

inline

This alternate constructor constructs a stored columns instance and immediately associates a given stored columns file with it by calling the open() function. Refer to the open() function for more information.

~StoredColumns()

StoredColumns::~StoredColumns ( )

inline

The destructor releases the association with a stored columns file established by the alternate constructor or the open() function, if there is any.

Member Function Documentation

close()

void StoredColumns::close

(

)

This function releases the association with a stored columns file established by the alternate constructor or the open() function, if there is any. After callig this function, it is allowed to call open() again.

columnNames()

const vector< string > & StoredColumns::columnNames ( ) const

inline

This function returns the names of the columns in the file. The length of the list corresponds to the number of columns. If no file is open, the list is enpty.

columnUnits()

const vector< string > & StoredColumns::columnUnits ( ) const

inline

This function returns the unit strings for the columns in the file, in the same order as the column names returned by columnNames(). If no file is open, the list is enpty.

nextRow()

const double * StoredColumns::nextRow ( )

inline

This function returns a pointer to a list of the column values in the next row, or the null pointer if there are no more rows or if no file is open. The returned pointer becomes invalid upon the next invocation of this function, or when the file is closed. The column values are listed in the order corresponding to the list returned by columnNames(). The function returns rows one by one, in the order they are stored in the file.

open()

void StoredColumns::open

(

string

filepath

)

This function associates a given stored columns input file with the stored columns instance. If such an association already exists, or if the open operations fails, this function throws a fatal error. The filename argument specifies the absolute file path of the input file, including the mandatory ".scol" filename extension.

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The documentation for this class was generated from the following file:

• StoredColumns.hpp