I have folowing problem:
(also,sorry on my awkward english)

need to save and read some data to/from db

for key i use next struct:
//KEY
struct key{
int key_part1;
int key_part2;
};

// I am ok with Key but have problem with Data

//DATA
struct subitem{
int num;
float sub2;
float sub3;
};

struct data{ //data struct
bool flag;
int num_item_in_vector;// number of items in vector
std::vector<subitem> vec;// vector thta hold ? subitem structs
};

my problem come to this:
how to put (and get) "struct data" to(from) database since that struct
conatains vector ?

can i just use:
//simplify function store data

void func(struct key kkey, struct data ddata){

Dbt dbKey(&kkey,sizeof(struct key));
Dbt dbData(&ddata,sizeof(struct data));

db>put(NULL,&dbKey,&dbData,0); // to store item in db

}

i have no idea how to retrive that data from db? is it just enough to
call:

Dbt dbKey(&kkey,sizeof(struct key);
Dbt dbData(&ddata,sizeof(struct data);
Dbc * tcur;

....
while(..){
tcur->get(&dbKey,&dbData,DB_NEXT))==0)
// will dbData contain valid data??? i(f key is valid)
....
....
....}
any suggestion are most welcome

tnx in advance

Of course, this is not working as I thought .

problem is in vector... need to marshall data from vector in
contiguous memory...

sugestion are still most wellcome




sinisa wrote:

Since BDB supports variable-sized records, just copy all the vector's
elements to a contiguous array and point a Dbt at it. To "unserialize"
after a get(), just reverse the process. The following struct might be
handy:

struct serial_data {
bool flag;
int num_item_in_vector;
struct subitems[]; // points to the memory just beyond this struct,
where the subitems are stored
};

Using this struct the serialize process would be (pass those structs by
reference!!!):

void put(struct key &kkey, struct data &ddata) {
// allocate enough space to hold everything
size_t size = ...;
char tmp[size]; // use new if size might ever be bigger than ~100

// cast it to a serial_data* to make life easier
// sizeof(tmp) > sizeof(serial_data) on purpose --
// you need space for the subitems
struct serial_data* tmp_data = (struct serial_data*) tmp;

// copy the flags and item count across

// use an STL algorithm like copy_n to copy the vector's elements
// into tmp_data->subitems[]

// point a Dbt at tmp (not ddata!) and call put()
}

The unserialize process would be similar:

void get(struct key &kkey, struct data &ddata) {
Dbt dbData, dbKey;

// call get()

struct serial_data* tmp_data = (struct serial_data*)
dbData.get_data();

// copy the flags and size across

// use an appropriate STL algorithm to fill the vector
// use the size you just read to avoid going out of bounds

// free the Dbt's memory (see the API ref)
}

Just watch out for alignment issues if your machine cares.

Ryan

tnx Ryan

Ryan wrote:

tnx Ryan

Ryan wrote: