Chapter 2I/O Classes
This chapter describes the following KCMS input/output (I/O)
classes:
KcsIO
KcsFile
KcsMemoryBlock
KcsSolarisFile
KcsXWindow
The KcsIO class provides a common interface for
I/O operations such as read and write. The KcsIO class
is a derivative of the KcsShareable class (see Chapter 1, KcsShareable Class). The KcsFile, KcsMemoryBlock, KcsSolarisFile, and KcsXWindow are derivatives of the KcsIO class. These
derivatives provide I/O for more specific types of data storage.
As you read this chapter, you will find it helpful to have access to
the following header files:
kcsio.h, kcsfile.h, kcsmblk.h, kcssolfi.h, and kcsxwin.h
kcsshare.h and kcsids.h
KcsIO Class
With a common interface, the KcsIO class maintains device-, platform-,
and transport-independent I/O functionality for all derivatives.
The header file for the class is kcsio.h. The constant
and #define identifiers for this class are defined in the kcsids.h header file as:
const KcsId KcsSharIOId = {(0x494F0000UL)}; /* 'IO' */
#define KcsSharIOIdd (0x494F0000UL) /* 'IO' */
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The enumerations and protected and public members are described, as
well as the member function override rules when deriving from this class.
Enumerations
The KcsIO class provides the following enumerations.
Table 2-1 KcsIO Enumerations
Enumeration | Description |
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enum KcsIOPosition {KCS_OFS, KCS_BOO,
KCS_CUR}; |
| Used for calls to setCursorPos(). KCS_OFS is relative
to beginning of I/O object+baseoffset. KCS_BOO is relative
to beginning of the I/O object. KCS_CUR is relative to
present I/O cursor. |
Protected Members
The KcsIO class provides the following protected
members.
Table 2-2 KcsIO Protected Members
Protected Member | Description |
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KcsStatus
aSysError(const char *callersName,
const char *sysName, KcsStatus stat,
const int sysErrCode); |
| A protected member that returns a KcsStatus object that contains the OS error in the causingError data member. Use callersName for debugging; it is recommended
that you change to a non-NULL value. |
Public Members
The KcsIO class provides the following public
members.
Table 2-3 KcsIO Public Members
Member Function | Description |
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virtual
KcsStatus absRead(const long index,
const long bytesWanted,
void *buffer,
const char *callersName = NULL); |
| Absolute read an I/O object already opened or allocated.
Supply a count of number of bytes to read and a buffer. |
virtual
KcsStatus absWrite(const long index,
const long numBytes2Write,
const void *buffer,
const char *callersName = NULL); |
| Absolute write to some number of bytes in numBytes2Write from the buffer to the data store at the current
position of the cursor |
virtual
KcsStatus copyData(KcsIO *anotherIO); |
| Copies all data in I/O object to anotherIO object. |
static KcsIO * createIO(KcsStatus *aStatus,
const KcsProfileDesc *aDesc); |
| Static method that creates an I/O object, by calling either
a KcsIO derivative constructor within the KCMS library
or a run-time loadable constructor. |
virtual
KcsStatus getEOF(long *theEOF) = 0; |
| Returns the end-of-file (EOF) position. |
virtual
long getOffset(); |
| Returns the permanent offset into the I/O object. |
virtual
KcsIOType getType() = 0; |
| Returns the type of I/O object. |
virtual
int isEqual(KcsIO *anotherIO) = 0; |
| Determines if this I/O object and another I/O object are
working on the same data stores. The base offsets must also be the same for
them to return true. |
KcsIO(KcsStatus *status,
const unsigned long absBaseOffset = 0); |
| Constructor that initializes the baseOffset
data member with the values passed in. |
| Destructor. |
virtual
KcsStatus relRead(const long bytesWanted,
void *buffer,
const char *callersName = NULL) = 0; |
| Reads bytesWanted from the I/O object
from the current position of the cursor. Positions the cursor after the last
byte read. |
virtual
KcsStatus relWrite(const long numBytes2Write,
const void *buffer,
const char *callersName = NULL) = 0; |
| Relative write of the number of bytes in numBytes2Write from the buffer to the data store
at the current position of the cursor. Positions the cursor after the last
byte written. |
virtual
KcsStatus replaceData(const unsigned long offset,
const unsigned long oldSize,
const void *buffer,
const unsigned long newSize,
const char *callersName = NULL); |
| Replaces bytes of different lengths in an
I/O object. Specifies where to start writing and size of old and new data.
If the old data is longer than the new data, the I/O object is compressed.
If the new data is longer than the old data, everything after the old data
is moved to the end of the I/O object. If an error occurs, the cursor is where
it was before the error occurred. |
virtual
KcsStatus setCursorPos(long position,
const KcsIOPosition mode= KCS_OFS,
const char *callersName = NULL) = 0; |
| Sets the I/O object cursor to a caller-supplied position. Positions the I/O object cursor to a specific
spot in the object. Mode is defined by the enum KcsFilePosition. |
virtual
KcsStatus setEOF(long theEOF) = 0; |
| Sets the EOF to a caller-supplied position. If the new
EOF is greater than the old EOF, the storage for the new space is undefined. |
virtual
void setOffset(long theOffset); |
| Sets the base offset to a specified position. |
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