---
name: "SharedFile"
section: "3cc"
platform: "linux"
package: "libcommoncpp2-dev"
version: "1.0.13-5"
release: "Debian 3.1 (Sarge)"
platforms: ["linux"]
url: "https://new.carta.tech/SharedFile"
---

# SharedFile(3cc)

This class defines a database I/O file service that can be shared by multiple processes. This class defines a database I/O file service that can be shared by multiple processes.

## NAME

SharedFile - This class defines a database I/O file service that can be shared by multiple processes. This class defines a database I/O file service that can be shared by multiple processes.

## SYNOPSIS

`#include <file.h>`

Inherits **RandomFile**.

### Public Methods

**SharedFile** (const char \*path)\
 *Open or create a new database file.* **SharedFile** (const SharedFile &file)\
 *Create a shared file as a duplicate of an existing shared file.* virtual **~SharedFile** ()\
 *Close and finish a database file.* **Error** **restart** (void)\
 *Restart an existing database; close and re-open.* **Error** **fetch** (char \*address=NULL, **ccxx\_size\_t** length=0, off\_t position=-1)\
 *Lock and Fetch a portion of the file into physical memory.* **Error** **update** (char \*address=NULL, **ccxx\_size\_t** length=0, off\_t position=-1)\
 *Update a portion of a file from physical memory.* **Error** **clear** (**ccxx\_size\_t** length=0, off\_t pos=-1)\
 *Clear a lock held from a previous fetch operation without updating.* **Error** **append** (char \*address=NULL, **ccxx\_size\_t** length=0)\
 *Add new data to the end of the file.* off\_t **getPosition** (void)\
 *Fetch the current file position marker for this thread.* bool **operator++** (void)\
 bool **operator--** (void)\

## DETAILED DESCRIPTION

This class defines a database I/O file service that can be shared by multiple processes. This class defines a database I/O file service that can be shared by multiple processes.

Each thread should access a dup of the database object, and mutex locks can be used to preserve transaction integrety if multiple threads are used.

SharedFile is used when a database may be shared between multiple processes. SharedFile automatically applies low level byte-range 'file locks', and provides an interface to fetch and release byte-range locked portions of a file.

**Author:**  David Sugar \<dyfet@ostel.com\>

## CONSTRUCTOR & DESTRUCTOR DOCUMENTATION

### SharedFile::SharedFile (const char \* path)

Open or create a new database file.

You should also use Initial.

**Parameters:**

- *path*

  *pathname of database to open.*

### SharedFile::SharedFile (const SharedFile & file)

*Create a shared file as a duplicate of an existing shared file.*

**Parameters:**

- *file*

  *original file.*

### virtual SharedFile::~SharedFile ()` [virtual]`

*Close and finish a database file.*

## MEMBER FUNCTION DOCUMENTATION

### Error SharedFile::append (char \* address = NULL, ccxx\_size\_t length = 0)

*Add new data to the end of the file.*

*Locks file during append.*

**Parameters:**

- *address*

  *address to use, or NULL if same as last I/O.*

- *length*

  *length to use, or 0 if same as last I/O.*

### Error SharedFile::clear (ccxx\_size\_t length = 0, off\_t pos = -1)

*Clear a lock held from a previous fetch operation without updating.*

**Returns:**  *errSuccess on success.*

**Parameters:**

- *length*

  *length to use, or 0 if same as last I/O.*

- *pos*

  *file position to use or -1 if same as last I/O.*

### Error SharedFile::fetch (char \* address = NULL, ccxx\_size\_t length = 0, off\_t position = -1)

*Lock and Fetch a portion of the file into physical memory.*

*This can use state information to fetch the current record multiple times.*

**Returns:**  *errSuccess on success.*

**Parameters:**

- *address*

  *address to use, or NULL if same as last I/O.*

- *length*

  *length to use, or 0 if same as last I/O.*

- *position*

  *file position to use -1 if same as last I/O.*

### off\_t SharedFile::getPosition (void)

*Fetch the current file position marker for this thread.*

**Returns:**  *file position offset.*

### bool SharedFile::operator++ (void)

### bool SharedFile::operator-- (void)

### Error SharedFile::restart (void)` [inline, virtual]`

*Restart an existing database; close and re-open.*

**Returns:**  *errSuccess if successful.*

*Reimplemented from* **RandomFile***.*

### Error SharedFile::update (char \* address = NULL, ccxx\_size\_t length = 0, off\_t position = -1)

*Update a portion of a file from physical memory.*

*This can use state information to commit the last read record. The current lock is also cleared.*

**Returns:**  *errSuccess on success.*

**Parameters:**

- *address*

  *address to use, or NULL if same as last I/O.*

- *length*

  *length to use, or 0 if same as last I/O.*

- *position*

  *file position to use or -1 if same as last I/O.*

## AUTHOR

*Generated automatically by Doxygen for CommonC++ from the source code.*