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Add lint-style FALLTHROUGH annotations to fallthrough cases. (in the parse engine and thus the output code) Document this, because the old output causes warnings with gcc10.
author David A. Holland
date Mon, 13 Jun 2022 00:04:38 -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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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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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