---
name: "ost_SharedFile"
section: "3"
platform: "linux"
package: "libcommoncpp2-doc"
version: "1.8.1-10"
release: "Debian 11 (Bullseye)"
platforms: ["linux"]
url: "https://new.carta.tech/ost_SharedFile"
---

# ost\_SharedFile(3)

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

## NAME

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

## SYNOPSIS

`#include <file.h>`

Inherits **ost::RandomFile**.

### Public Member Functions

**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** (caddr\_t address=NULL, **ccxx\_size\_t** length=0, off\_t position=-1)\
 Lock and Fetch a portion of the file into physical memory.  **Error** **update** (caddr\_t 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** (caddr\_t 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)\

### Additional Inherited Members

## Detailed Description

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

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

## Constructor & Destructor Documentation

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

Open or create a new database file. You should also use Initial.

**Parameters**

*path* pathname of database to open.

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

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

**Parameters**

*file* original file.

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

Close and finish a database file.

## Member Function Documentation

### Error ost::SharedFile::append (caddr\_t 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 ost::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 ost::SharedFile::fetch (caddr\_t 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 ost::SharedFile::getPosition (void)

Fetch the current file position marker for this thread.

**Returns**

file position offset.

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

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

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

Restart an existing database; close and re-open.

**Returns**

errSuccess if successful.

Reimplemented from **ost::RandomFile**.

### Error ost::SharedFile::update (caddr\_t 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

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