Question

I’m working with c++ and I am writing a budget program (I’m aware many are available–it’s just a learning project).

I want to save what I call a book object that contains other objects such as ‘pages’. Pages also contain cashflows and entries. The issue is that there can be any amount of entries or cashflows.

I have found a lot of information on saving data to text files but that is not what I want to do.

I have tried looking into using the boost library as I’ve been told serialization might be the solution to this problem. I’m not entirely sure which functions is boost are going to help or even what the proper ways are to use boost.

Most examples of binary files that I have seen are with objects that have fixed size members. For example, a point might contain an x value and a y value that are both doubles. This will always be the case so it is simple to just use sizeOf(Point).

So, I’m either looking for direct answers to this question or useful links to information on how to solve my problem. But please make sure you links are specific to the question.

I’ve also posted the same question on cplusplus

Answer 1

In general, there are two methods to store variable length records:

1. Store size integer first, followed by the data.
2. Store the data, append a sentinel character (or value) at the end.

C-style strings use the 2nd option.
For option one, the number contains the size of the data.

Optional Fields

If your considering relational database design for optional fields, you would have one table with the known or fixed records and another table containing an option field with the record ID.

A simpler route may be to go to something similar to XML: field labels.
Split your object into two sections: static fields and optional fields.
The static field section would be followed by an optional field section. The optional field section would contain the field name, followed by the field data. Read in the field name then the value.

I suggest you review your design to see if optional fields can be eliminated. Also, for complex fields, have them read in their own data.

Storing Binary Data

If the data is shared between platforms, consider using ASCII or textual representation.

Read up upon Endianess and also bit sizes. For example one platform could store its binary representation least significant byte first and use 32 bits (4 bytes). The receiving platform, 64-bit, most significant byte first, would have problems reading the data directly and would need to convert; thus losing any benefit from binary storage.

Similarly, floating point doesn’t fare well in binary either. There is also the loss of precision when converting between floating point formats.

When using optional fields in binary, one would use a sentinel byte or number for the field ID rather than a textual name.

Also, data in textual format is much easier to debug than data in binary format.

Consider using a Database

See At what point is it worth using a database?