Bart Torbert wrote:
For testing purposes it would be convenient to load dummy values into
a set of C structures. These structures are complex (in the sense of
a mix of data types), they are quite large (total number of elements)
and they will have a tendency to change over time.
I would be best if the dummy data was "meaningful", real dates in a
date field, a small number in the number field, a short string in a
text field, etc.
Is there a way to load the data without having to walk through each
element of each structure. I would be time consuming and fragile to
write a special function to load each structure as there are so many
and their exact content tends to change with frequent changes in the
software.
The ideal solution would be able to take a structure, loop through all
elements, for each element be able to determine its type and
dynamically assign the elment an appropriate value.
Is this doable?
No, in the sense that it is not possible to start from
struct s { int i; float f; double d; };
and somehow deduce "int, float, double."
With a little work, though, you can prepare a generic
description of a struct and write some code to process it.
You'd use something like
struct struct_layout {
enum { INT, FLOAT, DOUBLE, ..., END } type;
size_t offset;
};
struct struct_layout s_desc[] = {
{ INT, offsetof(struct s, i) },
{ FLOAT, offsetof(struct s, f) },
{ DOUBLE, offsetof(struct s, d) },
{ END, 0 }
};
You'd prepare a description like this for each struct type
of interest. Then to generate data for a particular struct
instance, you give your code a pointer to that instance and
a pointer to the matching description:
void fill_struct(void *sp, const struct struct_layout *dp);
struct s s_instance;
fill_struct (&s_instance, s_desc);
Observe that this technique is in fact more useful than
what you asked for. If "introspection" were somehow part of
C, it might at best tell you "int, float, double." But if
you prepare your own descriptions, you can go further and
tell what kinds of data these elements represent: Instead of
"int, float, double" you can have "birth_year, weight_kg,
annual_interest_rate."
In a large project it can become tedious to keep the
struct descriptions up-to-date as programmers modify the
structs themselves. If you're going to do a lot of this sort
of thing, it might be wise to generate both the struct
declarations and their corresponding definitions from a
little language invented for the purpose.
--
Er*********@sun.com 
