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<dd><pre class="Code2"><b><a name="85081">* {@@ 0}</a></b></pre>
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<dd><p class="Body"><a name="85082"> </a>The first <b class="symbol_lc">*</b> replaces the pointer with the value of <b class="symbol_lc">pOther</b>; the fragment in braces executes only if the pointer is not <b class="symbol_lc">NULL</b>. The <b>@@</b> fragment writes <b class="symbol_lc">x1</b> and <b class="symbol_lc">x2</b> to the tape, and the final <b>0</b> sets the pointer to <b class="symbol_UC">NULL</b> so that the <b>{...}</b> loop exits. Guarding this fragment in angle brackets (so that it executes with a local copy of the pointer), adding <b class="symbol_lc">+4</b> to move the pointer to <b class="symbol_lc">pOther</b>, and inserting this fragment into the example string, you have:</p>
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<dd><pre class="Code2"><b><a name="90847"><i class="textVariable">nodeAddr</i> * { @ &lt; +8 *$ &gt; &lt; +4 * {@@ 0} &gt; * }</a></b></pre>
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<hr><div class="CalloutCell"><a name="90857"><b class="symbol_UC"><font face="Helvetica, sans-serif" size="-1" class="sans">NOTE:  </font></b></a>Wind River Systems has developed a "Gopher generator" tool which generates gopher scripts from a C structure. This tool is not supported, but is available free of charge. It can be downloaded from the Wind River System WEB server (www.wrs.com).</div>
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<h4 class="H4"><i><a name="90849">The Gopher Result Tape</a></i></h4>
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<dd><p class="Body"><a name="85095"> </a>The Gopher result tape is a byte-packed data stream. The data is a series of pairs, each consisting of a type code and its associated data. The type codes are defined in the file <i class="textVariable">installDir</i><b class="file">/share/src/agents/wdb/wdb.h</b> as follows:<p class="table">

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<div class="CellBody"><a name="85098"> </a>GOPHER_UINT32</div>

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<div class="CellBody"><a name="85100"> </a>0</div>

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<div class="CellBody"><a name="85102"> </a>GOPHER_STRING</div>

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<div class="CellBody"><a name="85104"> </a>1</div>

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<div class="CellBody"><a name="85106"> </a>GOPHER_UINT16</div>

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<div class="CellBody"><a name="85108"> </a>2</div>

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<div class="CellBody"><a name="85110"> </a>GOPHER_UINT8</div>

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<div class="CellBody"><a name="85112"> </a>3</div>

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<div class="CellBody"><a name="85114"> </a>GOPHER_FLOAT32</div>

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<div class="CellBody"><a name="85116"> </a>4</div>

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<div class="CellBody"><a name="85118"> </a>GOPHER_FLOAT64</div>

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<div class="CellBody"><a name="85120"> </a>5</div>

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<div class="CellBody"><a name="85122"> </a>GOPHER_FLOAT80</div>

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<div class="CellBody"><a name="85124"> </a>6</div>

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<dd><p class="Body"><a name="85191"> </a>The tape is formatted as shown in <a href="c-wtx3.html#85131">Figure&nbsp;4-5</a>.<div class="frame">
<h4 class="EntityTitle"><a name="85131"><font face="Helvetica, sans-serif" size="-1" class="sans">Figure 4-5:&nbsp;&nbsp;Gopher Result Tape</font></a></h4>

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<h4 class="H4"><i><a name="85192">Sending the Gopher Script to the Target Agent</a></i></h4>
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<dd><p class="Body"><a name="85194"> </a>The Gopher interpreter on the target agent interprets and executes the Gopher script. Any tool or application can send a Gopher script to the target agent by using the appropriate WTX command. Both Tcl and C language APIs provide commands for this purpose.</p>
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<b class="HU-bullet"><li><a name="85196"> </a><font face="Helvetica, sans-serif" size="-1" class="sans">Tcl</font></li></b>
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<dd><p class="Body"><a name="85197"> </a>Our Gopher script assumes that <i class="textVariable">nodeAddr</i> is a pointer to the first node. To establish this pointer using Tcl, query the symbol table for the value of <b class="symbol_lc">nodeList</b>, and then send the Gopher script to the target agent using the Tcl procedure <b class="tclProc">wtxGopherEval</b>:</p>
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<dd><pre class="Code2"><b><a name="85198">set nodeList [lindex [wtxSymFind -name nodeList] 1] 
wtxGopherEval $nodeList * { @ &lt; +8 *$ &gt; &lt; +4 * {@@ 0} &gt; * }</a></b></pre>
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<dd><p class="Body"><a name="85200"> </a>Tcl interprets the Gopher result tape and returns a Tcl list consisting of just the data values. For our example, the Tcl API returns the following list:</p>
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<dd><pre class="Code"><b><a name="85201">    { <i class="textVariable">name1 value1 x11 x21 name2 value2 ... x1n x2n</i> )</a></b></pre>
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<dd><p class="Body"><a name="85202"> </a>For further information, see the online reference material under <b class="guiLabel"><font face="Helvetica, sans-serif" size="-1" class="sans">Tornado API Guide&gt;WTX Tcl Library</font></b>.</p>
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<b class="HU-bullet"><li><a name="85204"> </a><font face="Helvetica, sans-serif" size="-1" class="sans">C</font></li></b>
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<dd><p class="Body"><a name="85205"> </a>The procedure for sending the Gopher script using C involves a similar process. First use the C routine <b class="routine"><i class="routine">wtxSymFind</i></b><b>(&nbsp;)</b> to query the symbol table for the value of <b class="symbol_lc">nodeList</b>. Convert the value to a string, and then send this string, concatenated with the Gopher script, to the target agent using <b class="routine"><i class="routine">wtxGopherEval</i></b><b>(&nbsp;)</b>. C returns the byte-packed data stream without formatting it. <a href="c-wtx3.html#85212">Example&nbsp;4-1</a> shows how to submit the Gopher script and format the result tape. For further information, see the online reference material under <b class="guiLabel"><font face="Helvetica, sans-serif" size="-1" class="sans">Tornado API Guide&gt;WTX Tcl Library</font></b>.</p>
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<h4 class="EntityTitle"><a name="85212"><font face="Helvetica, sans-serif" size="-1" class="sans">Example 4-1:&nbsp;&nbsp;Evaluating a Gopher Script Using the C API</font></a></h4>
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<dd><pre class="Code"><b><a name="85213">/* find the starting address */ 
 
if ((pSymbol = wtxSymFind (hWtx, "nodeList", NULL, 0, 0, 0)) == NULL) 
    { 
    printf ("Could not find symbol\n"); 
    return; 
    } 
 
/* convert this value to a string */ 
 
sprintf (startAddress, "0x%p", pSymbol-&gt;value); 
 
/* free the symbol room */ 
 
wtxResultFree (hWtx, pSymbol); 
 
/* integrate this string into the Gopher script and execute it*/ 
 
sprintf (gopherCmd, "%s * { @ &lt; +8 *$ &gt; &lt; +4 * {@@ 0} &gt; * }",  
        startAddress); 
 
if ((pResult = wtxGopherEval (hWtx, gopherCmd)) == NULL) 
    { 
    printf ("gopher error: %s\n", wtxErrToMsg (hWtx, 
            wtxErrGet(hWtx))); 
    return; 
    } 
 
/* format the result tape */ 
 
STATUS formatResult 
    ( 
    WTX_GOPHER_TAPE   pTapeResult, 
    char *            pFinalResult 
    ) 
 
    { 
    int    targetByteOrder = wtxTargetEndianGet (hWtx); 
    int    needSwap        = targetByteOrder != HOST_BYTE_ORDER; 
    int    bufIx; 
 
    bufIx = 0; 
    while (bufIx &lt; pTapeResult-&gt;len) 
        { 
        char valbuf [20]; 
        UINT8 type          = pTapeResult-&gt;data [bufIx++]; 
        unsigned char *bufp = pTapeResult-&gt;data + bufIx; 
 
        switch (type) 
            { 
            case GOPHER_UINT32: 
                { 
                UINT32 rawVal = UNPACK_32 (bufp); 
                sprintf (valbuf, "%#x", SWAB_32_IF (needSwap, rawVal)); 
                strcat (pFinalResult, valbuf); 
                bufIx += sizeof (UINT32); 
                break; 
                } 
            case GOPHER_UINT16: 
                { 
                UINT16 rawVal = UNPACK_16 (bufp); 
                sprintf (valbuf, "%#x", SWAB_16_IF (needSwap, rawVal)); 
                strcat (pFinalResult, valbuf); 
                bufIx += sizeof (UINT16); 
                break; 
                } 
            case GOPHER_UINT8: 
                { 
                UINT8 rawVal = *bufp; 
                sprintf (valbuf, "%#x", rawVal); 
                strcat (pFinalResult, valbuf); 
                bufIx += sizeof (UINT8); 
                break; 
                } 
            case GOPHER_FLOAT32: 
                { 
                union 
                    { 
                    UINT32      i; 
                    float       f; 
                    } u; 
 
                UINT32 rawVal = UNPACK_32 (bufp); 
                u.i = SWAB_32_IF (needSwap, rawVal); 
                sprintf (valbuf, "%.8g", u.f); 
                strcat (pFinalResult, valbuf); 
                bufIx += sizeof (float); 
                break; 
                } 
            case GOPHER_FLOAT80: 
 
                /*  
                 * This one is trouble. We aren't able to represent 
                 * 80-bit floats on the host, so we just take the 
                 * upper 64 bits and convert to double.  
                 */ 
 
                if (targetByteOrder == LITTLE_ENDIAN) 
                    { 
                    /* skip over least significant 16 bits. */ 
   
                    bufIx += 2; 
                    bufp += 2; 
                    } 
   
                /* FALL THROUGH */ 
   
            case GOPHER_FLOAT64: 
                { 
                union 
                    { 
                    UINT32      i [2]; 
                    double      d; 
                    } u; 
   
                if (needSwap) 
                    { 
                    u.i [1] = SWAB_32 (UNPACK_32 (bufp)); 
                    u.i [0] = SWAB_32 (UNPACK_32 (bufp+4)); 
                    } 
                else 
                    { 
                    u.i [0] = UNPACK_32 (bufp); 
                    u.i [1] = UNPACK_32 (bufp+4); 
                    } 
 
                sprintf (valbuf, "%.16g", u.d); 
                strcat (pFinalResult, valbuf); 
                bufIx += sizeof (double); 
 
                /*  
                 * If target is big endian and we fell through the 80-bit 
                 * case, we need to advance over the least-significant 
                 * 16 bits which we have no way of converting.  
                 */ 
  
                if (type == GOPHER_FLOAT80 &amp;&amp; targetByteOrder == BIG_ENDIAN) 
                    bufIx += 2; 
 
                break; 
                } 
            case GOPHER_STRING: 
                { 
                strcat (pFinalResult, pTapeResult-&gt;data + bufIx); 
                bufIx += strlen (pTapeResult-&gt;data + bufIx) + 1; 
                } 
            } 
        } 
 
  return OK; 
  }</a></b></pre>
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