{"id":26,"date":"2013-07-19T03:53:30","date_gmt":"2013-07-19T03:53:30","guid":{"rendered":"https:\/\/praveenkatiyar.wordpress.com\/?p=26"},"modified":"2013-07-19T03:53:30","modified_gmt":"2013-07-19T03:53:30","slug":"packing-a-array-inside-a-variant-vc-6-0-series-3-of-n","status":"publish","type":"post","link":"https:\/\/praveenkatiyar.in\/blog\/index.php\/2013\/07\/19\/packing-a-array-inside-a-variant-vc-6-0-series-3-of-n\/","title":{"rendered":"Packing a array inside a VARIANT (VC++ 6.0) (Series 3 of N)"},"content":{"rendered":"

This is the third post about variant, in this post I I am going to explain, how an array of structures can be packed inside a VARIANT variable. suppose we have a structure as definition shown below.<\/p>\n

typedef struct MyStructType
{
    int nID ;
    long lVal ;
    double dblVal ;
    TCHAR szBuffer[255];
} MyStructType ;<\/font><\/p>\n

Packing  a array of structure inside a Variant<\/h3>\n

int  PackVariantWithStructArray(short nCnt, VARIANT * pVar )
{
    \/\/ TODO: Add your dispatch handler code here
    USES_CONVERSION ;<\/font><\/sup><\/font><\/p>\n

    \/\/Initialize the VARIANT (Type is SAFEARRAY of BYTE)
    VariantInit(pVar);
    pVar->vt = VT_ARRAY | VT_UI1 ;<\/font><\/sup><\/p>\n

    int nBufferSize = nCnt * sizeof ( MyStructType );<\/font><\/sup><\/p>\n

    \/\/ Define a safe array of nCnt Item and Starting index as 0
    SAFEARRAYBOUND safeBounds = { nBufferSize, 0};
   
    \/\/Create the Safe Array passing it the bounds
    SAFEARRAY* pSafeArray = SafeArrayCreate(VT_UI1, 1, &safeBounds);<\/font><\/sup><\/p>\n

    \/\/Get a pointer to the array data, This actually increments the array’s lock count)
    MyStructType * structArray = NULL;
    SafeArrayAccessData(pSafeArray, (void**)&structArray);
    for ( int i = 0 ; i < nCnt ; i++ )
    {
        CString strTmp ;
        strTmp.Format ( _T("This is Item %2d"), i );
        structArray[i].dblVal = (i +1) * 101.0 ;
        structArray[i].lVal = (i +1) * 11 ;
        structArray[i].nID = (i +1) ;
        _tcscpy ( structArray[i].szBuffer, strTmp) ;
    } <\/font><\/sup><\/p>\n

    \/\/ We are done wth populating the array Decrement the lock<\/font><\/sup><\/p>\n

     SafeArrayUnaccessData(pSafeArray);<\/font><\/sup><\/p>\n

    \/\/Assign our VARIANT out param with the array   
    pVar->parray = pSafeArray ;
    return nCnt ;
}<\/font><\/sup><\/p>\n

as it can be seen from the above code, here I have just created a byte buffer sufficient to accommodate the all structures, <\/p>\n

it involves following steps.<\/p>\n

    \n
  1. Allocating the desired temporary buffer space to hold the array of structures (that should be equivalent to (number of structure x size of structure), and filling that array with values one need to return. <\/li>\n
  2. creating a safe array of the desired (VT_U1)<\/font><\/strong> type. <\/li>\n
  3. copying the temporary buffer to the safe array of the variant. <\/li>\n
  4. free the memory allocated for temporary buffer. (avoid memory leaks). <\/li>\n<\/ol>\n

    Fetching a array of structure from a variant.<\/h4>\n

    MyStructType * UnPackVariantWithStructArray(short nCount, VARIANT var )
    {
        MyStructType *pBuffer = (MyStructType *) calloc ( nCount, sizeof (MyStructType)) ;  <\/font><\/p>\n

        USES_CONVERSION ;
        SAFEARRAY* pSafeArray  = var.parray ;
        \/\/Get a pointer to the array data, This actually increments the array’s lock count)
        MyStructType *structArray = NULL ;
        SafeArrayAccessData ( pSafeArray, (void**)&structArray );
        for ( int i = 0 ; i < nCount ; i++ )
        {
            pBuffer[ i].dblVal = structArray [i].dblVal  ;
            pBuffer[ i].lVal = structArray [i].lVal ;
            pBuffer[ i].nID = structArray [i].nID   ;
            pBuffer[ i].dblVal = structArray [i].dblVal  ;
            _tcscpy ( pBuffer[ i].szBuffer, structArray [i].szBuffer );
        }
        \/\/    We are done wth populating the array Decrement the array’s lock count
        SafeArrayUnaccessData(pSafeArray);
        return pBuffer ;
    }<\/font><\/p>\n

    this is a crude method, although there is a better method using type libraries, that I will explain in some other article.<\/p>\n","protected":false},"excerpt":{"rendered":"

    This is the third post about variant, in this post I I am going to explain, how an array of structures can be packed inside a VARIANT variable. suppose we have a structure as definition shown below. typedef struct MyStructType {     int nID ;     long lVal ;     double dblVal ;     TCHAR… Continue reading Packing a array inside a VARIANT (VC++ 6.0) (Series 3 of N)<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3,9,15],"tags":[],"class_list":["post-26","post","type-post","status-publish","format-standard","hentry","category-codeproject","category-interoperability","category-win32","entry"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/posts\/26","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/comments?post=26"}],"version-history":[{"count":0,"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/posts\/26\/revisions"}],"wp:attachment":[{"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/media?parent=26"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/categories?post=26"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/tags?post=26"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}