Re: Solving a template/struct issue
Alexander Adam wrote:
I've got this issue: I have a struct like this:
struct node
{
unsigned int m_code;
?? m_data;
unsigned int m_data_size;
};
Which is put into a list like std::list<node> myList;
Now the issue is with m_data. I want a general approach to store
anything into m_data no matter what it is.
WHY? What are you modeling using that approach?
It could be a list of
simple chars, unsigned ints or double or float or whatever.
Really? Whatever? An airplain and a tomato, in the same list?
My idea
was that I could create an array for m_data, filling it up with the
appropriate values but how'd I go about this?
Again, why? What's the point, so to speak?
Lets take a basic sample -- Let's say I want to store those values
into my m_data (each into one single struct):
double dv = 1.8464634...;
double* dv2 = new double[3];
dv2[0] = dv;
dv2[1] = dv;
dv2[2] = dv;
const char* cv = "Hello World...";
How can I store dv, cv and especially dv2 correctly into my m_data
field without wasting memory and without having to templatize the node
struct?
void*
And the next question of course is -- how can I correctly read back
those values into my variables with the best perfomance possible?
You would have to store the type information beside the 'm_data'
member, and fill that information with whatever so you can recognise
the type later. Then use a big 'switch' statement (or some other
means) to convert the void* back into a pointer to the object of the
right type.
Could anyone provide me some simple sample code or give some hints on
how to go about this? I've thought about creating an array of e.g.
unsigned char and pushing the data into it. Would that work? If yes,
how would that look like?
Ugly.
Btw, just something I care for interest -- why will std::list<node*>
take much more memory than std::list<node> that is, when manually
doing a new node(); -> list.push_back(pointer_to_node) it takes more
memory at all than when using a value of std::list<node>?
Yes.
V
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