How to assign an integer value to "key.data" in Berkeley DB using C

Question

Off lately I am working with Berkeley DB. I have seen examples wherein people have used "string" as values to "key.data" while creating a database using Berkeley DB. I want to assign an integer value to it. How can I do that? Should I create a structure with int member in it or is there any other way possible?

DBT key, data;
memset(&key, 0, sizeof(key));
memset(&data, 0, sizeof(data));
key.data = "fruit";
key.size = sizeof("fruit");

So instead of "fruit" above I want to assign an integer value. Any kind of help would be appreciated.

ubiyubix · Accepted Answer · 2011-08-25 18:15:26Z

2

DBT structures provide a void * field that you use to point to your data, and another field that identifies the data length. They can therefore be used to store anything from simple primitive data to complex structures so long as the information you want to store resides in a single contiguous block of memory.

See, http://download.oracle.com/docs/cd/E17076_02/html/gsg/C/DBEntry.html

To store integers, you would assign a pointer to an int to key.data, e.g.:

int x = 42;
key.data = &x;
key.size = sizeof(x);

answered Aug 25, 2011 at 18:15

ubiyubix

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4 Comments

Keith Thompson Over a year ago

Won't that cause problems if you read the database file on a system with different byte ordering?

user537670 Over a year ago

@bromfiets: i used the method you showed above....but when I am trying to print it....it returns me a different value if ((ret = dbp->put(dbp, NULL, &key, &data, 0)) == 0) { printf("db: %d: key stored.\n", (char*)&key.data);}

ubiyubix Over a year ago

@user537670 With &key.data you are taking the address of the pointer key.data. This is not necessary. key.data is already a pointer; cast it to be a pointer to an int and deference it, for example printf("key: %d\n", *(int *) key.data);

ubiyubix Over a year ago

@Keith Yes it does. You would have to take care of byte ordering in the application, e.g. always read and write in a certain byte order.

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