readRecord!

readRecord!(handle, holder, [offset=0], [length])

handle is a binary file handle.

holder is a table or a tuple with array elements of equal size.

offset (optional) specifies the starting row position.

length (optional) indicates the number of rows to be loaded.

Convert binary files to DolphinDB data objects. DolhinDB also provides the function writeRecord to covert DolphinDB data objects to binary files that can be used by other programs. The binary files should be row-based and each row should contain records with fixed data types and lengths. For example, if a binary file contains 5 data fields with the following type (length): char(1), boolean(1), short(2), int(4), long(8), and double(8), the function readRecord! will treat every 24 bytes as a new row. Similarly, the function writeRecord converts DolphinDB objects such as tables or tuples to binary files with the aforementioned format.

// create a file handle for reading records. The binary file a.bin contains 1000 records
f=file("c:/DB/a.bin")
t=table(1000:0, `PERMNO`PRC`VOL`SHROUT, `int`double`int`double)
f.readRecord!(t);
// output
1000

// similarily, we can load a binary file to a DolphinDB tuple object
f=file("c:/DB/a.bin")
t=loop(array, [int, double, int, double], 0, 500)
// create tuple t with 4 array elements. The size of each array is 500.
 f.readRecord!(t, 0, 500);
// read the first 500 rows
// output
500