Hitachi MK-96RD647-01 manual Reading Data, DatasetGet Function

Reading Data

reclen = datasetGet (datasetHandle, buf, buflen)

The datasetGet function reads one record from the specified dataset

(datasetHandle) and puts the record into a buffer (buf) of length buflen. The datasetGet function extracts only the data entity from each record and does not transfer the BL and RL bytes for variable-length records to the buffer. Table 6-2shows the datasetGet arguments and return values.

Table 6-2 DatasetGet Function

Item	Value	Type	Description
Argument	datasetHandl	DATASET_HAND	The datasetHandle value returned by the datasetOpen
	e	LE	function.
			Buffer area for storing the read data.
	buf
		char *	Size of the buffer area. If the record is larger than buflen or equal to zero,
	buflen
		long	datasetGet returns an error and does not transfer any data to the buf.
Return value	reclen	long	Data entity size transferred to the buffer
	-1		Error end

Figure 6-1shows the format requirements for variable-length records accessed by the datasetGet function. Each variable-length block must start with the two-byte BL field, and each variable-length record must start with the two- byte RL field. The datasetGet function automatically extracts the data entities without the BL and RL fields.

Block length Record length Data entity

Record length

Block Length

Record length Data entity

Record length

Block length format:

2 bytes	2 bytes
Block length	0x0000

	2 bytes	2 bytes
Record length format:	Record length	0x0000

Figure 6-1 Format Requirements for Reading Variable-Length Records

When the datasetGet function terminates successfully, it returns the length of the data entity read from the dataset. If the datasetGet function detects the end of dataset (EOF) or terminates unsuccessfully, it returns a value of -1. To get the error code information, execute the datasetGetLastError function (see section Acquiring Error Information). For example, when the datasetGet function detects EOF, datasetGetLastError will return DATASET_ERROR_END_OF_FILE.

Performing File Access Library (FAL) Operations 6-5

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