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Import AnaGram (near-)release tree into Mercurial.
author David A. Holland
date Sat, 22 Dec 2007 17:52:45 -0500
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1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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2 <HTML>
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3 <HEAD>
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4 <TITLE>Character Sink Class Definitions</TITLE>
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5 </HEAD>
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6
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7
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8 <BODY BGCOLOR="#ffffff" BACKGROUND="tilbl6h.gif"
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9 TEXT="#000000" LINK="#0033CC"
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10 VLINK="#CC0033" ALINK="#CC0099">
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11
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12 <P>
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13 <IMG ALIGN="right" SRC="../images/agrsl6c.gif" ALT="AnaGram"
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14 WIDTH=124 HEIGHT=30 >
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15 <BR CLEAR="all">
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16 Back to :
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17 <A HREF="../index.html">Index</A> |
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18 <A HREF="index.html">Class libraries for examples</A>
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19 <P>
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20
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21
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22 <IMG ALIGN="bottom" SRC="../images/rbline6j.gif" ALT="----------------------"
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23 WIDTH=1010 HEIGHT=2 >
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24 <P>
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25
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26 <H1>Character Sink Class Definitions</H1>
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27 <IMG ALIGN="bottom" SRC="../images/rbline6j.gif" ALT="----------------------"
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28 WIDTH=1010 HEIGHT=2 >
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29 <P>
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30 <BR>
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31 <H2>Introduction</H2>
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32
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33 A character_sink is an abstract class, from which are derived
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34 two useful classes, an output_file class and a
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35 string_accumulator class. The basic idea of a character sink
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36 is that it can be used as the generic output device for a
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37 process that generates characters. Other character_sink
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38 classes can easily be imagined, in particular, parsers that
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39 take character input.
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40 <P>
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41 Because character_sink is an abstract class, you cannot
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42 declare a character_sink. You may however declare a pointer
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43 to a character sink:
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44 <PRE>
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45 character_sink *sink;
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46 </PRE>
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47 Character sinks overload the "&lt;&lt;" operator for int, (char *)
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48 and (unsigned char *) operands and return a reference to the
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49 sink so that multiple operations are possible. For example:
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50 <PRE>
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51 *sink &lt;&lt; 'c' &lt;&lt; "xyz";
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52 </PRE>
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53 The important aspect of a character sink is that a stream of
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54 characters can be easily switched from one destination to
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55 another.
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56 <P>
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57 <BR>
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58
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59 <H2> The output_file Class </H2>
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60 The output_file class is derived from the character sink
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61 class. There are two initializers: one with no arguments,
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62 which simply sends characters on to stdout; and one which
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63 takes a file name as an argument. If the file can be opened,
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64 characters are sent to the file, otherwise, they go to
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65 stdout. For example:
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66 <PRE>
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67 output_file out; //sinks characters to stdout
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68 output_file out("foo.bar"); //sinks characters to foo.bar
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69 output_file out(NULL); //sinks characters to stdout
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70
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71 out &lt;&lt; "Hello, world" &lt;&lt; '!';
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72
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73 character_sink *sink = &out; // sink points to an output_file
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74 </PRE>
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75 Note, that unlike normal C++ stream I/O, there is no binary
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76 to ascii conversion involved.
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77 <P>
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78 <BR>
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79
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80 <H2> The string_accumulator Class </H2>
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81
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82 The string_accumulator is derived from the character sink
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83 class, so you may use it as a destination for any character
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84 stream. Rather than pass characters on, however, a
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85 string_accumulator saves them up for later use. A
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86 string_accumulator works like a push down stack. Each level
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87 of the stack consists of a string. When you add characters to
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88 a string_accumulator they are appended to the topmost string
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89 on the stack.
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90
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91 Operators are provided for the following functions:
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92 <UL>
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93 <LI> increment the stack level, thus starting a new string </LI>
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94 <LI> decrement the stack level, thus discarding the top string </LI>
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95 <LI> append a character or string to the top string </LI>
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96 <LI> remove the last character from the top string on the stack </LI>
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97 <LI> inspect or change characters on the stack. </LI>
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98 <LI> obtain a pointer to the top string on the stack </LI>
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99 <LI> concatenate the top strings on the stack </LI>
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100 <LI> obtain a permanent copy of the top string on the stack </LI>
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101 <LI> find the length of a string </LI>
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102 <LI> reset the string accumulator </LI>
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103 </UL>
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104 <P>
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105 <BR>
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106
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107 <H2> Declaring a string_accumulator </H2>
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108
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109 To declare a string_accumulator, you must specify the amount
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110 of storage to be reserved for string storage. If you wish you
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111 may also specify the maximum number of levels. If you do not
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112 specify the number of levels you will get just one level. For
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113 example:
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114 <PRE>
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115 string_accumulator sa(1000, 20);
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116 string_accumulator lsa(100);
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117 </PRE>
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118 provides for 1000 characters and 20 levels in sa but just 100
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119 characters in a single level in lsa.
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120 <P>
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121 <BR>
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122
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123 <H2> Changing Levels </H2>
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124
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125 The "++" operator has been overloaded to increment the stack
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126 level. You may pre-increment the level to begin accumulating a
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127 nested string of characters. For example:
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128 <PRE>
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129 ++sa;
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130 </PRE>
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131 To discard the top string on the stack, use the pre-decrement
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132 operator "--":
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133 <PRE>
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134 --sa;
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135 </PRE>
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136 The pre-increment and pre-decrement operators return a
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137 reference to the string_accumulator so that you may combine
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138 operations in a single expression:
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139 <PRE>
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140 ++sa &lt;&lt; "Hello, world!";
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141 </PRE>
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142 If you store characters on a stack without incrementing the
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143 level, they are appended to the string at the current level.
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144 In particular, if you declare a string_accumulator with only
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145 a single level, you need never increment or decrement it. You
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146 may, however, wish to use the reset operator.
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147 <P>
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148 Post-increment and post-decrement operators are also defined
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149 for convenience in use. Instead of returning a reference to
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150 the string_accumulator, however, they simply return a copy of
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151 the control structure (in its pre-decrement or
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152 pre-increment state) which allows read-only access to the
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153 content of the string_accumulator. This can nevertheless be
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154 quite useful:
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155 <PRE>
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156 char *top_string = copy(sa--);
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157 </PRE>
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158 <P>
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159 <BR>
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160
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161 <H2> Appending Characters to a String </H2>
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162
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163 To append characters you may use the overloaded "&lt;&lt;"
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164 operator, which also returns a reference to the string
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165 accumulator so you may combine operations:
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166 <PRE>
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167 sa &lt;&lt; "Hello, world" &lt;&lt; '!';
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168 </PRE>
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169 To start a new string and append characters use the
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170 pre-increment operator as well:
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171 <PRE>
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172 ++sa &lt;&lt; "Hello, world" &lt;&lt; '!';
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173 </PRE>
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174 <P>
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175 <BR>
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176
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177 <H2> Removing Characters from a String </H2>
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178
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179 To pop off the last character on the top string:
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180 <PFRE>
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181 int c;
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182 sa &lt;&lt; c;
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183 </PRE>
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184 <P>
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185 <BR>
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186
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187 <H2> Accessing the Content of a String </H2>
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188
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189 To inspect or change the k'th character from the top of the
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190 stack:
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191 <PRE>
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192 int c = sa[k];
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193 sa[k] = '!';
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194 </PRE>
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195 If k is zero you get the last character on topmost string
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196 in the string_accumulator.
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197 <P>
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198 To get a pointer to the top string on the stack, use the
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199 (char *) cast operator:
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200 <PRE>
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201 char *p;
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202 p = (char *) sa;
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203 </PRE>
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204 <BR>
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205
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206 <H2> Concatenating Strings </H2>
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207
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208 To concatenate the top two strings on the stack, use
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209 concat():
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210 <PRE>
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211 concat(sa);
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212 </PRE>
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213 <BR>
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214
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215 <H2> Making a Permanent Copy of a String </H2>
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216
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217 To make a copy of the top string on the stack, use copy():
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218 <PRE>
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219 char *p = copy(sa);
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220 </PRE>
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221 Note that copy differs greatly from (char *), in that copy
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222 allocates storage for a new copy of the string. When you are
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223 done with it you should delete it:
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224 <PRE>
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225 delete [] p;
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226 </PRE>
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227 Note that copy() does not remove the string from the stack.
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228 Use "--" to discard the string from the stack.
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229 <P>
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230 <BR>
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231
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232 <H2> Finding the Length of a String </H2>
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233
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234 To find the length of the top string on the stack, use
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235 size():
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236 <PRE>
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237 unsigned n = size(sa);
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238 </PRE>
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239 Like strlen, size does not count the terminating null
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240 character.
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241 <P>
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242 <BR>
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243
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244 <H2> Resetting a string_accumulator </H2>
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245
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246 The overloaded function reset() may be applied to a
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247 string_accumulator to reset it to its initial state:
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248 <PRE>
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249 reset(sa);
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250 </PRE>
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251 reset returns a reference to the string accumulator so that
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252 you may reset it and append text in a single statement:
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253 <PRE>
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254 reset(sa) &lt;&lt; "Hello, world!";
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255 </PRE>
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256 <P>
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257 <BR>
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258
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259
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260 <IMG ALIGN="bottom" SRC="../images/rbline6j.gif" ALT="----------------------"
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261 WIDTH=1010 HEIGHT=2 >
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262 <P>
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263 <IMG ALIGN="right" SRC="../images/pslrb6d.gif" ALT="Parsifal Software"
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264 WIDTH=181 HEIGHT=25>
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265 <BR CLEAR="right">
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266
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267 <P>
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268 Back to :
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269 <A HREF="../index.html">Index</A> |
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270 <A HREF="index.html">Class libraries for examples</A>
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271
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272 <P>
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273 <ADDRESS><FONT SIZE="-1">
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274 AnaGram parser generator - examples<BR>
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275 Class libraries - Character sink class definitions<BR>
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276 Copyright &copy; 1993-1999, Parsifal Software. <BR>
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277 All Rights Reserved.<BR>
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278 </FONT></ADDRESS>
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279
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280 </BODY>
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281 </HTML>