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",$len;<BR>
printf EncD "\nstrncat((STRPTR )(&buffer[%d]),tempbuffer,%d);",
<BR>
$from-1,$len;
<BR>
}<BR>
if ($vtype =~ /int/) {<BR>
{<BR>
if ($len == 1)
<BR>
{
<BR>
printf
EncD "\nsp->%s %%= 10;", $vname;<BR>
printf
EncD "\ntempbuffer[%d] = (char)('0' + sp->%s);",
<BR>
$from-1,$vname;
<BR>
printf
EncD "\ntempbuffer[%d] = 0; ",$from;<BR>
}
<BR>
else<BR>
{
<BR>
printf EncD "\nsprintf(tempbuffer,\"%%d%d\",(sp->%s));",$len,$vname;
<BR>
printf EncD "\ntempbuffer[%d]=
0; ",$len;<BR>
}
<BR>
printf EncD "\nstrncat((STRPTR
)(&buffer[%d]),tempbuffer,%d);",<BR>
$from-1,$len;
<BR>
}<BR>
}<BR>
} # end of subroutine.</FONT></TT>
</BLOCKQUOTE>
<H2><A NAME="WritingtheDecoder"><B><FONT SIZE=5 COLOR=#FF0000>Writing
the Decoder</FONT></B></A></H2>
<P>
The decoder source file is created in almost exactly the same
way that the encoder file is created. The preamble for the decoder
file includes the <TT><FONT FACE="Courier">#include</FONT></TT>
statement for the <TT><FONT FACE="Courier">P286.h</FONT></TT>
header file, which is also being created. It also makes a reference
to the <TT><FONT FACE="Courier">padTo80</FONT></TT> function in
the encoder file (should this extra function be required).
<P>
The decoder file also generates code to extract a substring from
another string given the offset and length to extract. The function
may be used on systems that have a broken <TT><FONT FACE="Courier">strncpy</FONT></TT>
(just like my old, in-house version of the C compiler for a Motorola
6809E microprocessor).
<P>
Here's the code to generate the decoder source file preamble:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">sub startDecoderFile {<BR>
print (DECD "\/**\n* C source file to decode records.",
<BR>
" \nDon't edit this file\n ",
<BR>
"*/\n",<BR>
'#include "p286.h" ',<BR>
"\n",<BR>
"\n/* The outgoing buffer must be
81 chars! */",<BR>
"\nextern void padTo80(STRPTR buffer);
\n",<BR>
"\n",<BR>
"\n/* The outgoing buffer must also
be 81 chars! */",<BR>
"\nvoid substr(STRPTR buffer,STRPTR
cut,int offset, int len)\n{\n",<BR>
"int i,j; \nj = offset;\n",
<BR>
"for(i=len;i<80;i++) cut[i] =
buffer[j]; \n ",<BR>
"cut[len] = 0; /* NULL terminate
the string*/",<BR>
"\n} /* end of padding function */\n",
<BR>
"\n");<BR>
}</FONT></TT>
</BLOCKQUOTE>
<P>
Each <TT><FONT FACE="Courier">RECORD</FONT></TT> and <TT><FONT FACE="Courier">ENDREC</FONT></TT>
pair in the input file causes a call to the Perl subroutines <TT><FONT FACE="Courier">startDecoderFunction()</FONT></TT>
and <TT><FONT FACE="Courier">closeDecoderFunction()</FONT></TT>,
respectively. The first subroutine creates the preamble to decode
a string into a structure. The second subroutine prints the closing
brace for a function. The code for the two functions is shown
here:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">sub startDecoderFunction {<BR>
my($vname) = @_; #
Pick up name of record.<BR>
print DECD "\n/*: ";<BR>
print DECD "\n** Generated by Perl
script -- Avoid editing ";<BR>
print DECD "\n** The outgoing buffer
must also be 81 chars!";<BR>
print DECD "\n*/\n";<BR>
printf DECD "void decode_%s_type(P286_%s_PTR
sp,STRPTR buffer)\n{",<BR>
$vname, $vname;
<BR>
print DECD "\nSTRPTR cp; \n";
<BR>
print DECD "register int i; \n";
<BR>
print DECD "char tempbuffer[80];\n";
<BR>
}<BR>
<BR>
sub closeDecoderFunction {<BR>
print DECD "\n} /* End of decoding
function */ \n";<BR>
}</FONT></TT>
</BLOCKQUOTE>
<P>
Finally, the <TT><FONT FACE="Courier">decodeVariable</FONT></TT>
function is called when a variable is encountered. The type of
variable dictates how to read the value from a substring in the
incoming buffer. The name of the variable is set to be a scalar
or the member of an array before the call is made. Therefore,
the Perl subroutine simply uses the value of <TT><FONT FACE="Courier">$vname</FONT></TT>
verbatim:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">sub decodeVariable {<BR>
my ($vname,$vtype,$from,$to,$fmt) = @_;
<BR>
my $len = $to - $from + 1;
<BR>
printf DECD "\n";<BR>
if ($vtype =~ /char/)<BR>
{<BR>
printf DECD "\nstrncpy(sp->%s,(STRPTR
)(&buffer[%d]),%d);",<BR>
$vname,$from-1,$len;
<BR>
printf DECD "\nsp->%s[%d]=
0; ",$vname,$len;<BR>
}<BR>
if ($vtype =~ /double/)<BR>
{<BR>
printf DECD "\nstrncpy(tempbuffer,(STRPTR
)(&buffer[%d]),%d);",<BR>
$from-1,$len;
<BR>
printf DECD "\ntempbuffer[%d]=
0; ",$len;<BR>
printf DECD "\nsscanf(tempbuffer,\"%%%sf\",&(sp->%s));",
$fmt,$vname;<BR>
}<BR>
if ($vtype =~ /int/)<BR>
{<BR>
printf DECD "\nstrncpy(tempbuffer,(STRPTR
)(&buffer[%d]),%d);",<BR>
$from-1,$len;
<BR>
printf DECD "\ntempbuffer[%d]=
0; ",$len;<BR>
printf DECD "\nsscanf(tempbuffer,\"%%%dd\",&(sp->%s));",$len,$vname;
<BR>
}<BR>
}</FONT></TT>
</BLOCKQUOTE>
<H2><A NAME="PuttingItTogether"><B><FONT SIZE=5 COLOR=#FF0000>Putting
It Together</FONT></B></A></H2>
<P>
Here are the input and output files generated from the code fragments
shown previously. The input file shown here has only five records
in it. The actual file had 52 record types, and I applied the
same methodology to three types of similar formats. Here is a
breakdown of the listings:
<UL>
<LI><FONT COLOR=#000000>Listing 31.2. The header file generated
from Perl.</FONT>
<LI><FONT COLOR=#000000>Listing 31.3. The encoder file </FONT><TT><FONT FACE="Courier">P286enc.c</FONT></TT>.
<LI><FONT COLOR=#000000>Listing 31.4. The encoder file </FONT><TT><FONT FACE="Courier">P286dec.c</FONT></TT>.
<LI><FONT COLOR=#000000>Listing 31.5. The full listing for the
code generator.</FONT>
</UL>
<P>
<HR>
<BLOCKQUOTE>
<B>Listing 31.2. The </B><TT><B><FONT FACE="Courier">P286.h</FONT></B></TT><B>
header file.<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT><FONT FACE="Courier"> 1 #ifndef P286_HDRS<BR>
2 #define P286_HDRS 1<BR>
3 #define STRPTR char *<BR>
4<BR>
5 #define P286_H0001_RECTYPE 0<BR>
6<BR>
7 typedef struct p286_H0001_type {<BR>
8 char SurveyType[53]; /* 29 80 */<BR>
9 }P286_H0001_TYPE,*P286_H0001_PTR;<BR>
10<BR>
11 #define P286_H0010_RECTYPE 1<BR>
12<BR>
13 typedef struct p286_H0010_type {<BR>
14 int numPatterns; /* 6 7 */<BR>
15 int sblInUse; /* 8 8 */<BR>
16 int sattInUse; /* 9 9 */<BR>
17 int numVessels; /* 10 10 */<BR>
18 int numDatum; /* 11 11 */<BR>
19 int offsetMode; /* 12 12 */<BR>
20 }P286_H0010_TYPE,*P286_H0010_PTR;<BR>
21<BR>
22 #define P286_H011_RECTYPE 2<BR>
23<BR>
24 typedef struct p286_H011_type {<BR>
25 int datumId; /* 5 5 */<BR>
26 char spheroidName[19]; /* 6 23 */<BR>
27 char datumName[19]; /* 24 41 */<BR>
28 double semimajorAxis; /* 42 53 */<BR>
29 double conversionFactor; /* 66 77 */<BR>
30 double inverseFlattening; /* 66 77 */<BR>
31 }P286_H011_TYPE,*P286_H011_PTR;<BR>
32<BR>
33 #define P286_E3100_RECTYPE 3<BR>
34<BR>
35 typedef struct p286_E3100_type {<BR>
36 double velprop; /* 6 12 */<BR>
37 int srcNdx[5]; /* from 13 15 */
<BR>
38 int dstNdx[5]; /* from 16 18 */
<BR>
39 double slant[5]; /* from 19 25
*/<BR>
40 }P286_E3100_TYPE,*P286_E3100_PTR;<BR>
41<BR>
42 #endif</FONT></TT>
</BLOCKQUOTE>
<HR>
<HR>
<BLOCKQUOTE>
<B>Listing 31.3. The encoder file </B><TT><B><FONT FACE="Courier">P286enc.c</FONT></B></TT><B>.
<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT><FONT FACE="Courier"> 1 /*** C source file to encode
records.<BR>
2 Don't edit this file<BR>
3 */<BR>
4 #include "p286.h"<BR>
5<BR>
6 /* The incoming buffer must be 81 chars! */<BR>
7 void padTo80(STRPTR buffer)<BR>
8 {<BR>
9 int i,ln;<BR>
10 ln = strlen(buffer);<BR>
11 for(i=ln;i<80;i++) buffer[i] = ' ';<BR>
12 buffer[81] = 0; /* NULL terminate the string*/
<BR>
13 } /* end of padding function */<BR>
14<BR>
15<BR>
16 /*:<BR>
17 ** Generated by Perl script -- Avoid editing<BR>
18 */<BR>
19 void encode_H0001_type(STRPTR buffer,P286_H0001_PTR sp)
<BR>
20 {<BR>
21 STRPTR ncp;<BR>
22<BR>
23 STRPTR cp;<BR>
24 register int i;<BR>
25 char tempbuffer[80];<BR>
26<BR>
27<BR>
28 /* Encode:char,SurveyType,29,80,52, */<BR>
29 cp = (STRPTR )&(buffer[28]);<BR>
30 for (i=0; i< 52;i++)<BR>
31 buffer[28 + i] = sp->SurveyType[i];
<BR>
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