RWFileManager(3C++) RWFileManager(3C++)
NameRWFileManager - Rogue Wave library class
Synopsis
typedef long RWoffset ;
typedef unsigned long RWspace; // (typically)
#include <rw/filemgr.h>
RWFileManager f("file.dat");
Description
Class RWFileManager allocates and deallocates storage in a disk file,
much like a "freestore" manager. It does this by maintaining a linked
list of free space within the file. Note: Class RWFileManager inherits
class RWFile as a public base class; hence all the public member
functions of RWFile are visible to RWFileManager. They are not listed
here. If a file is managed by an RWFileManager then reading or writing
to unallocated space in the file will have undefined results. In
particular, overwriting the end of allocated space is a common problem
which usually results in corrupted data. One way to encounter this
problem is to use binaryStoreSize() to discover the amount of space
needed to store an RWCollection. For most purposes, the storage size of
an RWCollection is found using the RWCollectable method
recursiveStoreSize().
Persistence
None
Public Constructor
RWFileManager(const char* filename, const char* mode = 0);
Constructs an RWFileManager for the file with path name filename using
mode mode. The mode is as given by the Standard C library function
fopen(). If mode is zero (the default) then the constructor will attempt
to open an existing file with the given filename for update (mode "rb+").
If this is not possible, then it will attempt to create a new file with
the given filename (mode "wb+"). If the file exists and is not empty,
then the constructor assumes it contains an existing file manager; other
contents will cause an exception of type RWExternalErr to be thrown. If
no file exists or if an existing file is empty, then the constructor will
attempt to create the file (if necessary) and initialize it with a new
file manager. The resultant object should be checked for validity using
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RWFileManager(3C++) RWFileManager(3C++)
function isValid(). A possible exception that could occur is RWFileErr.
Public Member Functions
RWoffset
allocate(RWspace s);
Allocates s bytes of storage in the file. Returns the offset to the
start of the storage location. The very first allocation for the file is
considered "special" and can be returned at any later time by the
function start(). A possible exception that could occur is RWFileErr.
void
deallocate(RWoffset t);
Deallocates (frees) the storage space starting at offset t. This space
must have been previously allocated by a call to allocate(). The very
first allocation ever made in the file is considered "special" and cannot
be deallocated. A possible exception that could occur is RWFileErr.
RWoffset
endData();
Returns an offset just past the end of the file.
RWoffset
start();
Returns the offset of the first space ever allocated for data in this
file. If no space has ever been allocated, returns RWNIL. This is
typically used to "get started" and find the rest of the data in the
file.
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