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Some minor updates for 15 years later.
author David A. Holland
date Tue, 31 May 2022 01:45:26 -0400
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1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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2
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3 <HTML>
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4 <HEAD>
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5 <TITLE>C Parsers - Macro preprocessor and C Parser </TITLE>
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6 </HEAD>
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7
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8
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9 <BODY BGCOLOR="#ffffff" BACKGROUND="tilbl6h.gif"
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10 TEXT="#000000" LINK="#0033CC"
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11 VLINK="#CC0033" ALINK="#CC0099">
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12
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13 <P>
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14 <IMG ALIGN="right" SRC="../../images/agrsl6c.gif" ALT="AnaGram"
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15 WIDTH=124 HEIGHT=30 >
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16 <BR CLEAR="all">
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17 Back to :
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18 <A HREF="../../index.html">Index</A> |
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19 <A HREF="index.html">Macro preprocessor overview</A>
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20 <P>
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21
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23 <IMG ALIGN="bottom" SRC="../../images/rbline6j.gif" ALT="----------------------"
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24 WIDTH=1010 HEIGHT=2 >
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25 <P>
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26
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27 <H1>C Parsers - Macro preprocessor and C Parser </H1>
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28
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29 <IMG ALIGN="bottom" SRC="../../images/rbline6j.gif" ALT="----------------------"
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30 WIDTH=1010 HEIGHT=2 >
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31 <P>
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32 <BR>
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33
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34 Two C grammars are provided with this example: <tt>jrc.syn</tt> is a
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35 translation of a <tt>yacc</tt> grammar for C created by James A.
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36 Roskind. <tt>krc.syn</tt> is a grammar adapted from Kernighan and
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37 Ritchie, Section A13.
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38 <P>
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39 Both grammars use semantically determined productions to
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40 distinguish between typedef names and identifiers, however,
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41 neither grammar has been adapted to take advantage of this
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42 capability to resolve many of the problems associated with
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43 typedef names.
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44 <P>
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45 In order to parse simple examples successfully, it was
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46 necessary to create a rudimentary capability to recognize
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47 typedef names. Such capabilities were incorporated into each
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48 grammar. Note that the scope handling is inadequate for
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49 production use.
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50 <P>
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51 In <tt>jrc.syn</tt>, the typedef token causes a flag to be set. When
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52 the identifier in a declaration is encountered, the flag is
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53 interrogated. The complication is the possible interposition
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54 of field names within a struct or union which could be
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55 inadvertently marked as typedef names. To avoid this, the
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56 flag is stored on encountering a struct or union and
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57 restored when the danger is past.
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58 <P>
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59 In <tt>krc.syn</tt>, the treatment of typedefs is marginally less
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60 inelegant. Storage class attributes are accumulated in a bit
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61 mask. As identifiers are encountered in the declaration
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62 statement they are pushed onto a multilevel stack, <tt>id_stack</tt>.
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63 When struct or union declarations are encountered, the level
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64 of the id_stack is incremented. When the danger is past, the
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65 level is decremented so that identifiers stacked in the
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66 course of parsing the struct or union are discarded.
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67 Eventually, when the statement is complete, all the
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68 identifiers that have been found are popped from <tt>id_stack</tt>
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69 and given the appropriate storage class attribute.
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70 <P>
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71 Both grammars are set up so that the name of the parser is
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72 <tt>cc()</tt>.
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73 Each
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74 syntax file contains member function definitions for the
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75 class <tt>c_parser</tt>. They are identical except for the
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76 initialization of the typedef logic. The definition of the
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77 class <tt>c_parser</tt> is found in <tt>MPP.H</tt>.
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78 <P>
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79 <B>Note:</B> Until AnaGram 2.40, the parsers were set up
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80 so both would emit the files <tt>cc.cpp</tt> and
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81 <tt>cc.h</tt>. This caused problems for AnaGram 2.40's more
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82 automated build and test system. As of this writing,
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83 <tt>krc.syn</tt> is used by default; to use <tt>jrc.syn</tt>
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84 you must change the <tt>#include</tt> near the top of
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85 <tt>mpp.h</tt> to include <tt>jrc.h</tt>. With luck, this
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86 annoyance will be cleared up in a future release.
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87 <P>
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88 It should be noted that the KRC grammar has at least one
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89 bug. It will not recognize function declarations of the
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90 form:
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91 <PRE>
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92 foo(int);
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93 </PRE>
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94 It will, however, recognize
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95 <PRE>
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96 int foo(int);
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97 </PRE>
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98 This problem appears to be inherent in the grammar published
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99 in K &amp; R.
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100 <P>
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101 <BR>
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102
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103
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104 <IMG ALIGN="bottom" SRC="../../images/rbline6j.gif" ALT="----------------------"
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105 WIDTH=1010 HEIGHT=2 >
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106 <P>
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107 <IMG ALIGN="right" SRC="../../images/pslrb6d.gif" ALT="Parsifal Software"
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108 WIDTH=181 HEIGHT=25>
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109 <BR CLEAR="right">
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110
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111 <P>
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112 Back to :
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113 <A HREF="../../index.html">Index</A> |
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114 <A HREF="index.html">Macro preprocessor overview</A>
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115
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116 <P>
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117 <ADDRESS><FONT SIZE="-1">
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118 AnaGram parser generator - examples<BR>
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119 C Parsers - Macro preprocessor and C Parser <BR>
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120 Copyright &copy; 1993-1999, Parsifal Software. <BR>
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121 All Rights Reserved.<BR>
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122 </FONT></ADDRESS>
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123
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124 </BODY>
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125 </HTML>
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126