NNDB

Introduction:
NNDB is a C++ library that provides in-memory data storage and retrieval in a way that feels natural for C++/STL. The syntax is easy to use and understand, with some similarities to SQL.

Examples:
Here is an example of NNDB syntax:
nndb::Table my_table;
my_table.Insert( nndb::Values("NNDB first row", 47));
nndb::ResultSet result_set = nndb::Select(nndb::select_star, my_table);

The above code does something similar to SQL:
CREATE TABLE my_table (col0 VARCHAR( ... ), col1 INT);
INSERT INTO my_table( col0, col1 ) VALUES ("NNDB first row", 47);
SELECT * FROM my_table;

You can use the result of your select with the following code:
nndb::ResultSet::const_iterator begin_it = result_set.begin();
const nndb::Values& first_row = *begin_it;
assert(nndb::Field(first_row) == "NNDB first row");
assert(nndb::Field(first_row) == 47);

Features:
NNDB offers useful features that are available in databases, some of them include:
- CREATE TABLE
- INSERT INTO table VALUES
- SELECT * FROM table
- SELECT ... WHERE ...
- SELECT ... ORDER BY ...
- SELECT ... WHERE ... ORDER BY ...
- Unique indexes

However, there are some useful features that NNDB does not have yet but might include in a future update:
- SELECT col0, col1 ...
- SELECT ... JOIN ...
- Non-unique indexes
- Save/load to disk

In contrast, there are several features that NNDB will never have, such as:
- Multiple simultaneous users
- User security
- Multiple processes.

Conclusion:
NNDB is an excellent choice for developers looking for a C++ library that provides in-memory storage and retrieval functionality. It is easy to use and understand and is an excellent alternative for developers who do not need the advanced functionality of traditional databases.