Big-Data-HPC-Platform/docs/ECLR_mods/SpecStruc-BeginC++.xml

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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<sect1 id="BEGINCplus_Structure">
  <title>BEGINC++ Structure<indexterm>
      <primary>BEGINC++ Structure</primary>
    </indexterm></title>

  <para><emphasis>resulttype funcname </emphasis><emphasis
  role="bold">(</emphasis><emphasis> parameterlist </emphasis><emphasis
  role="bold">) := BEGINC++<indexterm>
      <primary>BEGINC++</primary>
    </indexterm></emphasis><emphasis role="bold">
  </emphasis><emphasis></emphasis></para>

  <para><emphasis> code</emphasis><emphasis role="bold"> </emphasis></para>

  <para><emphasis role="bold">ENDC++<indexterm>
      <primary>ENDC++</primary>
    </indexterm>;</emphasis></para>

  <informaltable colsep="0" frame="none" rowsep="0">
    <tgroup cols="2">
      <colspec align="left" colwidth="122.40pt" />

      <colspec />

      <tbody>
        <row>
          <entry><emphasis>resulttype</emphasis></entry>

          <entry>The ECL return value type of the C++ function.</entry>
        </row>

        <row>
          <entry><emphasis>funcname</emphasis></entry>

          <entry><para>The ECL attribute name of the function.</para></entry>
        </row>

        <row>
          <entry><emphasis>parameterlist</emphasis></entry>

          <entry>The parameters to pass to the C++ function.</entry>
        </row>

        <row>
          <entry><emphasis>code</emphasis></entry>

          <entry>The C++ function source code.</entry>
        </row>
      </tbody>
    </tgroup>
  </informaltable>

  <para>The <emphasis role="bold">BEGINC++ </emphasis>structure makes it
  possible to add in-line C++ code to your ECL. This is useful where string or
  bit processing would be complicated in ECL, and would be more easily done in
  C++, typically for a one-off use. For more commonly used C++ code, writing a
  plugin would be a better solution (see the <emphasis role="bold">External
  Service Implementation</emphasis> discussion).</para>

  <para><emphasis role="bold">WARNING: This feature could create memory
  corruption and/or security issues, so great care and forethought are
  advised—consult with Technical Support before using.</emphasis></para>

  <sect2 id="ECL_to_Cplus_Mapping">
    <title>ECL to C++ Mapping</title>

    <para>Types are passed as follows:</para>

    <programlisting>//The following typedefs are used below:
typedef unsigned size32_t;
typedef wchar_t UChar; [ unsigned short in linux ]</programlisting>

    <para>The following list describes the mappings from ECL to C++. For
    embedded C++ the parameters are always converted to lower case, and
    capitalized in conjunctions (see below).</para>

    <programlisting><emphasis role="bold">ECL                  C++ [Linux in brackets]</emphasis>
BOOOLEAN xyz         bool xyz
INTEGER1 xyz         signed char xyz
INTEGER2 xyz         signed short xyz
INTEGER4 xyz         signed int xyz
INTEGER8 xyz         signed __int64 xyz [ long long ]
UNSIGNED1 xyz        unsigned char xyz
UNSIGNED2 xyz        unsigned short xyz
UNSIGNED4 xyz        unsigned int xyz
UNSIGNED8 xyz        unsigned __int64 xyz [ unsigned long long xyz ]
REAL4 xyz            float xyz
REAL/REAL8 xyz       double xyz
DATA xyz             size32_t lenXyz, void * xyz
STRING xyz           size32_t lenXyz, char * xyz
VARSTRING xyz        char * xyz;
QSTRING xyz          size32_t lenXyz, char * xyz
UNICODE xyz          size32_t lenXyz, UChar * xyz
VARUNICODE xyz       UChar * xyz
DATA&lt;nn&gt; xyz         void * xyz
STRING&lt;nn&gt; xyz       char * xyz
QSTRING&lt;nn&gt; xyz      char * xyz
UNICODE&lt;nn&gt; xyz      UChar * xyz
SET OF ... xyz       bool isAllXyz, size32_t lenXyz, void *  xyz</programlisting>

    <para>Note that strings of unknown length are passed differently from
    those with a known length. A variable length input string is passed as a
    number of characters, not the size (i.e. qstring/unicode), followed by a
    pointer to the data, like this (size32_t is an UNSIGNED4):</para>

    <programlisting>string ABC -&gt; size32_t lenAbc, const char * abc;
unicode ABC -&gt; size32_t lenABC, const UChar * abc;</programlisting>

    <para>A dataset is passed as a size/pointer pair. The length gives the
    size of the following dataset in bytes. The same naming convention is
    used:</para>

    <programlisting>dataset(r) ABC -&gt; size32_t lenAbc, const void * abc</programlisting>

    <para>NOTE: variable length strings within a record are stored as a 4 byte
    number of characters, followed by the string data.</para>

    <para>Sets are passed as a set of parameters (all, size, pointer):</para>

    <programlisting>set of unsigned4 ABC -&gt; bool isAllAbc, size32_t lenAbc, const void * abc</programlisting>

    <para>Return types are handled as C++ functions returning the same types
    with some exceptions. The exceptions have some extra initial parameters to
    return the results in:</para>

    <programlisting><emphasis role="bold">ECL                C++ [Linux in brackets]</emphasis>
DATA xyz           size32_t &amp; __lenResult, void * &amp; __result
STRING xyz         size32_t &amp; __lenResult, char * &amp; __result
QSTRING xyz        size32_t &amp; __lenResult, char * &amp; __result
UNICODE xyz        size32_t &amp; __lenResult, UChar * &amp; __result
DATA&lt;nn&gt; xyz       void * __result
STRING&lt;nn&gt; xyz     char * __result
QSTRING&lt;nn&gt; xyz    char * __result
UNICODE&lt;nn&gt; xyz    UChar * __result
SET OF ... xyz     bool __isAllResult, size32_t &amp;  __lenResult,
                      void * &amp; __result</programlisting>

    <para>For example,</para>

    <programlisting>STRING process(STRING value, INTEGER4 len)</programlisting>

    <para>has the prototype:</para>

    <programlisting>void process(size32_t &amp; __lenResult, char * &amp; __result,
             size32_t lenValue, char * value, int len);</programlisting>
  </sect2>

  <sect2 id="Available_Options">
    <title>Available Options</title>

    <para><emphasis role="bold">#option pure</emphasis>By default, embedded
    C++ functions are assumed to have side-effects, which means the generated
    code won't be as efficient as it might be since the calls can't be shared.
    Adding #option pure inside the embedded C++ <emphasis>code</emphasis>
    causes it to be treated as a pure function without side effects.</para>

    <para><emphasis role="bold">#option once</emphasis>Indicates the function
    has no side effects and is evaluated at query execution time, even if the
    parameters are constant, allowing the optimizer to make more efficient
    calls to the function in some cases.</para>

    <para><emphasis role="bold">#option action</emphasis>Indicates side
    effects, requiring the optimizer to keep all calls to the function.</para>

    <para><emphasis role="bold">#body</emphasis> Delimits the beginning of
    executable code. All <emphasis>code</emphasis> that precedes #body (such
    as #include) is generated outside the function definition; all code that
    follows it is generated inside the function definition.</para>

    <para>Example:</para>

    <programlisting>//static int add(int x,int y) {
INTEGER4 add(INTEGER4 x, INTEGER4 y) := BEGINC++
  #option pure
  return x + y;
ENDC++;
         
OUTPUT(add(10,20));
          
//static void reverseString(size32_t &amp; __lenResult,char *  &amp; __result,
// size32_t lenValue,char * value) {
STRING reverseString(STRING value) := BEGINC++
   size32_t len = lenValue;
   char * out = (char *)rtlMalloc(len);
   for (unsigned i= 0; i &lt; len; i++)
        out[i] = value[len-1-i];
   __lenResult = len;
   __result = out;
ENDC++;
OUTPUT(reverseString('Kevin'));
// This is a function returning an unknown length string via the
// special reference parameters __lenResult and  __result
         
//this function demonstrates #body, allowing #include to be  used
BOOLEAN nocaseInList(STRING search,
          SET OF STRING values) := BEGINC++
#include &lt;string.h&gt;
#body 
  if (isAllValues)
    return true; 
  const byte * cur = (const byte *)values; 
  const byte * end = cur + lenValues; 
  while (cur != end) 
  { 
  unsigned len = *(unsigned *)cur; 
  cur += sizeof(unsigned); 
  if (lenSearch == len &amp;&amp; memicmp(search, cur, len) == 0) 
      return true; 
  cur += len; 
  } 
  return false;
ENDC++;
          
//and another example, generating a variable number of Xes
STRING buildString(INTEGER4 value) := BEGINC++
   char * out = (char *)rtlMalloc(value);
   for (unsigned i= 0; i &lt; value; i++)
     out[i] = 'X';
     __lenResult = value;
     __result = out;
ENDC++;</programlisting>

    <para>See Also: <link linkend="External_Service_Implementation">External Service Implementation</link></para>
  </sect2>
</sect1>