CODEWITHSUNDEEP
c++cassandra
Boris Pitel
Boris Pitel

Reputation: 63

How to bind decimal type in Cassandra C++ DataStax

I am using DataStax Cassandra driver I am trying to insert progrmatically rows into cassandra table. One of the columns if the table is of decimal type. My query is

insert into thetable (id, price) values (?,?)

I prepare the statement cass_session_prepare, and then i bind cass_statement_bind_int32_by_name the id.

The issue starts when i try to bind decimal. The prototype of the method is

  CassError cass_statement_bind_decimal ( statement, index, varint, varint_size, scale )

where varint is pointer to bytes, varint_size number of bytes, and scale is scale.

So, finally my question is how to calculate the content of the byte array i am supposed to pass to the method? First i naively thought that if I pass just a character representation of number ( "1234.56") it would work. But of course i doesn't work. Now I understand that byte array I supposed to pass is something what is called BigInteger in Java. But how to convert string or double to this BigInteger array I don't know. I don't think Cassandra driver API provides anything that can help me with this conversion. So, if somebody can help me in resolving this issue I would be very grateful

Upvotes: 1

Views: 281

Answers (1)

Fero
Fero

Reputation: 406

There are many libraries out there you can utilize to perform the conversion:

If you look into the integration tests for the DataStax C/C++ driver, you will find a rudimentary BigNumber implementation that utilizes the OpenSSL BIGNUM library. This implementation does not perform arithmetic operations, but will allow you to easily convert the byte array (with scale) into a BigNumber for comparison and display.

NOTE: The OpenSSL BIGNUM implementation is known to be slower than many of the other libraries. A more complete implementation can be found in the DataStax PHP driver GitHub repository which uses the GMP library.

Upvotes: 2

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