IO
[casa core modules (libcasa)]

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Detailed Description

Basic classes and global functions for IO and object persistency.

See below for an overview of the classes in this module.

Review Status

Reviewed By:

UNKNOWN

Date Reviewed:

before2004/08/25

Synopsis

This module provides the basic IO functionality for the AIPS++ classes. There are two IO mechanisms:

1. Class AipsIO provides the object persistency mechanism. The templated global functions in (see AipsIOCarray.h (file="AipsIOCarray.h::AipsIOCarray")) form a little layer upon AipsIO. They provide the means to put or get a C-style array of any type.
2. Class ByteSinkSource and its ancestors provide a general IO mechanism.

Both use the underlying IO framework which define where and how the data is written. The how-part is defined by classes derived from TypeIO as shown in the OMT diagram. There are three such classes:

1. CanonicalIO reads/writes data in canonical (machine-independent) format. This should be used when data are meant to be exportable. It uses the conversion functions in class

   CanonicalConversion .

2. RawIO reads/writes data in native (machine-dependent) format. This can be used when data are not exported.
3. ConversionIO reads/writes in an external format as defined at construction time. This can be used when the external format can be one of several (e.g. VAX or IBM for a WSRT archive tape). In this way the format has to be defined only once and thereafter is it handled correctly by the polymorphism mechanism.

The where-part is defined by classes derived from ByteIO as shown in the OMT diagram. There are a few such classes:

1. RegularFileIO uses a regular file to hold the data. Internally it uses FilebufIO (see below).
2. FilebufIO uses the stdio system to do IO in a buffered way. It uses an internal buffer to do physical IO only when needed. See the description of C-functions like fopen, fread or do man stdio for more information.
3. FiledesIO uses the UNIX IO-functions like open, read to do IO directly. It does not use an internal buffer. Instead it always do a physical IO. It is meant for IO operations where large chunks of a file are accessed and for IO on sockets, pipes, etc.\.
4. MemoryIO uses a (possibly expandable) buffer in memory to hold the data.

The IO framework is easily expandable. Once can for instance think of a class AsciiIO derived from TypeIO to hold data in ASCII format.
A class TapeIO could be derived from ByteIO to access tape files. This class can also contain functions to skip to a tape file, which the user can call directly. Similarly a class RemoteTapeIO could be developed.

Modules
	IO_internal_classes
	Internal IO classes and functions.
Classes
class	casa::AipsIO
	AipsIO is the object persistency mechanism of AIPS++. More...
struct	casa::AipsIOCarray_global_functions_AipsIOCarray
	Templated functions to get/put a C-style array from/into AipsIO. More...
class	casa::BaseSinkSource
	Shared base class for ByteSink and ByteSource. More...
struct	casa::BucketCache_global_functions_BucketCache_CallBack
	Define the type of the static read and write function. More...
class	casa::BucketCache
	Cache for buckets in a part of a file. More...
class	casa::ByteIO
	Abstract base class for IO on a byte stream. More...
class	casa::ByteSink
	Class for write-only access to data in a given format. More...
class	casa::ByteSinkSource
	Class for read/write access to data in a given format. More...
class	casa::ByteSource
	Class for read-only access to data in a given format. More...
class	casa::CanonicalIO
	Class for IO in canonical format. More...
class	casa::ConversionIO
	Class for IO in a converted format. More...
class	casa::FilebufIO
	Class for buffered file IO. More...
class	casa::FiledesIO
	Class for IO on a file descriptor. More...
class	casa::FileLocker
	Class to handle file locking. More...
class	casa::LargeFilebufIO
	Class for buffered IO on a large file. More...
class	casa::LargeFiledesIO
	Class for IO on a large file descriptor. More...
class	casa::LargeRegularFileIO
	Class for IO on a regular large file. More...
class	casa::LECanonicalIO
	Class for IO in little endian canonical format. More...
class	casa::LockFile
	Class to handle file locking and synchronization. More...
class	casa::MemoryIO
	Class for IO to a memory buffer. More...
class	casa::RawIO
	Class for IO in local format. More...
class	casa::RegularFileIO
	Class for IO on a regular file. More...
class	casa::StreamIO
	Class for IO on connection oriented socket. More...
class	casa::TapeIO
	Class for IO on a tape device. More...
class	casa::TypeIO
	Abstract base class for IO of data in a type-dependent format. More...

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