Access to binary databases

One: Store data in binary form in the database

Here, we store the coordinates of multiple points in the form of a one-dimensional array of float:

Idea: First convert the float array into a char array, then convert it to SAFEARRAY and store it in BLOB data, and then store it in the Image field in the database.

1: Convert the float array to a char array:

Function

Input: Flaot contains the number of n in a one-dimensional array array

Output: Char one-dimensional array

Specific code:

Char *ptval = new char[n*sizeof (float)];//used to store the converted Char array

for (int i = 0; i<n; i++)

{

Char *m = new char[sizeof (float)];

Float temp = f[i];//Removes an object from the float array every time

memcpy (m,&temp,sizeof (float));//convert float to a 4-byte char array

int j = 0;

Inserts the converted char array into the corresponding position of the Ptval array

while (j<sizeof (float))

{

PTVAL[4*I+J] = M[j];

j + +;

}

Delete m;

}

2: Convert char array to SAFEARRAY array type, then convert to BLOB array type and import Database

Input: Char array corresponds to the number of bytes blobsize the location of the corresponding field in the database Icol

Function: Converts a char array to binary and inserts into the database

Specific code:

Long I, RTN;

char *pmove = NULL;

_variant_t Vval;

Safearraybound rgsabound[1];

SAFEARRAY *PSA = NULL;

Pmove = Ptval;

1. Create a SafeArray object

Rgsabound[0].llbound = 0; Defines the lower bound of an array

Rgsabound[0].celements = blobsize; To define the size of an array element

PSA = SafeArrayCreate (vt_ui1,1,rgsabound);

for (i = 0; i < blobsize; i++)

{

if (FAILED (SafeArrayPutElement (PSA, &i, pmove++))

return (0);

}

Storing data as BLOB type

VVAL.VT = Vt_array | VT_UI1;

Vval.parray = PSA;

Adding binary data to a database

Try

{

Fields *pfields = M_precordset-> getfields ();

Field *pfield = pfields-> GetItem (icol);

Pfield->appendchunk (Vval);

M_precordset->getfields ()->getitem (icol)->appendchunk (vval);

}

Catch error

catch (_com_error &e)

{

AfxMessageBox (E.description ());

return (0);

}

return (1);

Second: Extracting data from the database

Idea: Take the data from the database into a buffer of a char array, then decode and restore to a float array

1: Extracting data from the database into the buffer

Implementation process:

Fields *pflds;

Pflds = M_precordset->getfields ();

Long ldatasize = Pflds->getitem ("Data")->actualsize;

_variant_t num = pflds->getitem ("num")->getvalue ();

int n = num.intval;

Char *pbuf;

if (fp!=null) Delete FP;

fp = new Float[n];

float test;

if (ldatasize>0)

{

_variant_t val = Pflds->getitem ("Data")->getchunk (ldatasize);

if (VAL.VT = = (vt_array| VT_UI1))

{

PBuf = new Char[ldatasize+1];

char *pmove = NULL;

Safearrayaccessdata (Val.parray, (void * *) &pmove);

memcpy (pbuf,pmove,ldatasize); Copy data to buffer Pbuf

Safearrayunaccessdata (Val.parray);

Remove data from the database into the float array:

Implementation process:

for (int i = 0; i<n; i++)

{

Char *m = new CHAR[4];

int j = 0;

while (J<4)

{

M[J] = Pbuf[4*i+j];

j + +;

}

memcpy (&test,m,4);

Fp[i] = test;

Delete m;

}

delete [] pBuf;

}

Access to binary databases