Re: object serialization

James Kanze <>
21 Apr 2007 02:23:03 -0700
On Apr 21, 2:40 am, William <> wrote:

Why not just write the data in some data format? Serialization seems
to be the wrong level of abstraction, not only in C++ but also in
other languages. Convert your data to a readable maybe even
standardized format and the receivers will be happy.

Well, I'm only doing it so I can pass the data from a process to a
thread I just launched.

If the two threads are in the same process, you don't need
serialization, since they share common memory. (You will need
to ensure synchronized access, however.)

So it's all sorta in the same name space. It's
just my libraries are in C++ and I was hoping to serialize the data
nativly in c++ so that when I copy it into my obj-c objects, i've be
most of the way done w/ performance benefits.

In fact, you're concerned with communicating between two
languages, rather than between two processes or machines.
That's a different kettle of fish entirely; depending on the
representations used, it can vary from trivial (from C++ to C)
to very complicated (C++ to Cobol, perhaps). Serialization is
one solution, of course, but it is rarely the simplest or the
most efficient. Basically, when going from language A to
language B:

 -- If possible, use data with compatible formats. This is what
    makes C++ to C work so well; C++ more or less requires a
    large category of data types to have a format compatible
    with C, so all you have to do is pass a pointer to it to the
    C function.

 -- Failing that, you'll have to convert the data somehow. The
    conversions can be more or less complicated: when going from
    C++ to Fortran, for example, most of the basic types (int,
    float, etc.) will be compatible, so all you have to worry
    about is the fact that all Fortran parameters are by
    reference, that Fortran arrays are row major, rather
    than column major (but that can possibly be handled just by
    declaring them differently) and strings---Fortran's
    character type is not generally compatible with either
    std::string or char[]. If the target is Cobol, on the other
    hand, you may end up having to convert double's to BCD, and
    what have you.

 -- Finally, of course, if you already have serialization
    routings available in both languages, you can use them. Be
    aware, however, that what this really means is converting
    C++ date to a neutral, third format, and then converting
    this format back to the format in the other language. And
    that the neutral, third format conforms to a number of
    constraints which generally make it less efficient to
    convert to and from than other formats.

If the serialization is already present and handy in both
languages, or if it is or will be necessary anyway,
serialization is certainly an option to be considered.
Otherwise, however, it is by far the least efficient, both where
it always counts (your time and effort), and in terms of

James Kanze (Gabi Software) email:
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