Subj : store collections of strings in tdb or gdbm
To   : comp.programming
From : Lasse Kliemann
Date : Fri Oct 07 2005 10:22 pm

Greetings,

my data is organized as follows:

- There are several records.
- Each record consists of a fixed number of strings. Strings may 
  contain arbitrary characters, even null characters. I use the 
  stralloc implementation (http://cr.yp.to/lib/stralloc.html) to 
  realize this. In particular, string length is limited by the size of 
  an unsigned int.
- A key is associated with each record. Keys are also given as 
  strallocs.

The data shall be stored in a database like tdb 
(http://sourceforge.net/projects/tdb/), which has an interface very 
similar to that of gdbm.  To this end, each record has to be encoded in 
a structure like this (taken from tdb's manual pages):

typedef struct {
  char *dptr;
  size_t dsize;
} TDB_DATA;

I cannot simply concatenate the strings and put them into the dptr, 
because I would not find their ends and beginnings later (because the 
strings may contain null characters).

My idea so far for each record:

- Get the decimal representation of all the lengths of the strings in 
  the record.
- Write these into dptr, as null-terminated strings.
- Then write all the strings into dptr.

It is obvious how to get the strings back from this encoding.


My questions now are:

- How elegant is my approach?
- Is the conversion into the decimal representation necessary, or can I 
  write the lengths of the strings as unsinged ints into dptr? Would 
  this be portable?
- Hasn't this been done before and exists in form of a library?


Thanks for your advice!
Lasse

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