{"id":21,"date":"2013-07-17T18:35:15","date_gmt":"2013-07-17T18:35:15","guid":{"rendered":"https:\/\/praveenkatiyar.wordpress.com\/?p=21"},"modified":"2013-07-17T18:35:15","modified_gmt":"2013-07-17T18:35:15","slug":"packing-a-array-inside-a-variant-vc-6-0-series-1-of-n","status":"publish","type":"post","link":"https:\/\/praveenkatiyar.in\/blog\/index.php\/2013\/07\/17\/packing-a-array-inside-a-variant-vc-6-0-series-1-of-n\/","title":{"rendered":"Packing a array inside a VARIANT (VC++ 6.0) (Series 1 of N)"},"content":{"rendered":"

VARIANTs are versatile data types, they can hold any type of value, apart from that they can hold array of different types. In this post I am going to explain how can you pack a array of bytes, inside a variant variable.<\/p>\n

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

Packing  a array of bytes<\/h4>\n

int GetVariantWithByteBuffer (int nBufferSize, VARIANT FAR* pVar)
{<\/p>\n

    \/* here size of buffer desired (nBufferSize<\/strong>) has been passed to the function, which can be determined before hand. *\/<\/p>\n

\/* Creating a temporary buffer to hold the values one need to return and filling that buffer. fill buffer, this buffer can be filled some other ways too, reading from a file or reading from some hardware or whatever  here it has been filled from values 1 – 255*\/<\/font><\/strong><\/p>\n

     BYTE *pBuffer = (BYTE *) calloc ( nBufferSize, sizeof (BYTE))<\/font><\/strong> ; 
     for ( int i = 0 ;  i < nBufferSize<\/strong>; i++ ) pBuffer [i] = ( i + 1 ) % 256 ;  <\/p>\n

<\/font><\/strong><\/p>\n

     \/* Creating a variant to return, which can hold the safe array of bytes .*\/<\/font><\/strong><\/p>\n

     SAFEARRAY FAR* psa ;
     psa = SafeArrayCreateVector (VT_UI1, 0, nBufferSize); 
<\/strong><\/font>      if(psa == NULL)    return \u20131 ;  
      
     \/* Copying the temporary buffer to the variant to return *\/<\/font><\/strong><\/p>\n

     VariantInit ( pVar ) ; <\/p>\n

     pVar->parray = psa;
     pVar->vt = VT_ARRAY | VT_UI1 ;<\/strong><\/font> 
     memcpy ( pVar-><\/font><\/strong>parray->pvData , pBuffer, nBufferSize <\/strong>* sizeof (BYTE)<\/strong><\/font> ) ;  
<\/font><\/strong><\/p>\n

    \/* free the temporary buffer *\/<\/font><\/strong><\/p>\n

    free ( pBuffer ) ; <\/p>\n

    \/* return the number of elements  this variant hold. *\/<\/font><\/strong>
    return nBufferSize<\/strong>;<\/p>\n

}<\/p>\n

as it can be seen from the above code, it involves following steps.<\/p>\n

    \n
  1. Allocating the desired temporary buffer space to hold the array of bytes, and filling that array with values one need to return. <\/li>\n
  2. creating a safe array of the desired (VT_UI1)<\/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 bytes from a variant.<\/h4>\n

    BYTE * GetByteBufferFromVariant (int nBufferSize, VARIANT var )
    {<\/p>\n

        \/* here size of buffer desired (nBufferSize<\/strong>) has been passed to the function, which can help us determine the size of the buffer required. *\/<\/p>\n

        BYTE *pBuffer = (BYTE *) calloc ( nBufferSize, sizeof (BYTE))<\/font><\/strong> ;  
        memcpy ( pBuffer, var.parray->pvData, nBufferSize <\/strong>* sizeof (BYTE)<\/strong><\/font> ) ;  
        return pBuffer <\/strong>;<\/p>\n

    }<\/p>\n

    In  a similar fashion array of some other simple types can be  packed in a variant. the following table describes the data types for different simple types.<\/p>\n\n\n\n\n\n\n\n\n\n\n
    S.N.<\/font><\/strong><\/td>\nData Type<\/font><\/strong><\/td>\nValue of vt<\/font><\/strong> <\/td>\n<\/tr>\n
    1<\/td>\nBYTE <\/td>\nVT_ARRAY | VT_UI1 <\/td>\n<\/tr>\n
    2<\/td>\nSHORT (2 byte signed integer )<\/td>\nVT_ARRAY | VT_I2 <\/td>\n<\/tr>\n
    3<\/td>\nUSHORT (2 byte unsigned integer )<\/td>\nVT_ARRAY | VT_UI2 <\/td>\n<\/tr>\n
    4<\/td>\nINT (4 byte signed integer )<\/td>\nVT_ARRAY | VT_I4 <\/td>\n<\/tr>\n
    5<\/td>\nUINT (4 byte unsigned integer )<\/td>\nVT_ARRAY | VT_UI4 <\/td>\n<\/tr>\n
    6<\/td>\nFLOAT ( 4 byte float value)<\/td>\nVT_ARRAY|VT_R4<\/td>\n<\/tr>\n
    7<\/td>\nDOUBLE (8 byte double value)<\/td>\nVT_ARRAY|VT_R8<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

     <\/p>\n

    using the table above one can pack array of above defined types, to variant, these conversion is useful in middleware scenario<\/strong>. in the next article I will explain how to pack array of strings and array of structure<\/strong> inside a variant.<\/p>\n","protected":false},"excerpt":{"rendered":"

    VARIANTs are versatile data types, they can hold any type of value, apart from that they can hold array of different types. In this post I am going to explain how can you pack a array of bytes, inside a variant variable. Packing  a array of simple types inside a Variant Packing  a array of… Continue reading Packing a array inside a VARIANT (VC++ 6.0) (Series 1 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":[3,11,15],"tags":[],"class_list":["post-21","post","type-post","status-publish","format-standard","hentry","category-codeproject","category-mfc","category-win32","entry"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/posts\/21","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=21"}],"version-history":[{"count":0,"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/posts\/21\/revisions"}],"wp:attachment":[{"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/media?parent=21"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/categories?post=21"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/tags?post=21"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}