1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> |
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2 | <HTML> |
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3 | <HEAD> |
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4 | <TITLE>Source</TITLE> |
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5 | <LINK REL="stylesheet" HREF="../../../../boost.css"> |
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6 | <LINK REL="stylesheet" HREF="../theme/iostreams.css"> |
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7 | </HEAD> |
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8 | <BODY> |
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9 | |
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10 | <!-- Begin Banner --> |
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11 | |
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12 | <H1 CLASS="title">Source</H1> |
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13 | <HR CLASS="banner"> |
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14 | |
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15 | <!-- End Banner --> |
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16 | |
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17 | <H2>Definition</H2> |
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18 | |
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19 | <P> |
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20 | A Source is a <A HREF="device.html">Device</A> whose <A HREF="../guide/modes.html">mode</A> refines <A HREF="../guide/modes.html#input">input</A>. |
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21 | </P> |
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22 | |
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23 | <H2>Description</H2> |
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24 | |
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25 | <P>A Source provides read-access to a sequence of characters of a given type. In general, a Source may expose this sequence in two ways:</P> |
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26 | |
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27 | <OL> |
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28 | <LI STYLE="list-style-type:lower-roman"> |
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29 | by defining a member function <CODE>read</CODE>; or |
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30 | </LI> |
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31 | <LI STYLE="list-style-type:lower-roman"> |
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32 | by defining a member function <CODE>input_sequence</CODE> returning a pair of pointers delimiting the sequence in its entirety. |
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33 | </LI> |
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34 | </OL> |
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35 | |
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36 | <P>As a special case, Boost.Iostreams treats standard input streams as Sources. (For details, see <A HREF="../functions/read.html"><CODE>read</CODE></A>.)</P> |
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37 | |
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38 | <P>The mode of a Source is <A HREF="../guide/modes.html#input"><CODE>input</CODE></A> or one of its refinements.</P> |
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39 | |
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40 | <H2>Note</H2> |
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41 | |
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42 | <P>To be usable with the streams and stream buffers provided by the Boost Iostreams library, Sources must model <A HREF="blocking.html">Blocking</A>. |
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43 | |
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44 | <H2>Example</H2> |
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45 | |
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46 | <P> |
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47 | A model of Source can be defined as follows: |
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48 | </P> |
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49 | |
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50 | <PRE CLASS="broken_ie"><SPAN CLASS="keyword">struct</SPAN> Source { |
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51 | <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="keyword">char</SPAN> char_type; |
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52 | <SPAN CLASS="keyword">typedef</SPAN> source_tag category; |
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53 | std::streamsize read(<SPAN CLASS="keyword">char</SPAN>* s, std::streamsize n) |
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54 | { |
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55 | <SPAN CLASS="comment">// Read up to n characters from the input |
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56 | // sequence into the buffer s, returning |
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57 | // the number of characters read, or -1 |
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58 | // to indicate end-of-sequence.</SPAN> |
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59 | } |
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60 | };</PRE> |
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61 | |
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62 | <P> |
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63 | Here <CODE>source_tag</CODE> is a <A HREF="../guide/traits.html#category_tags">category tag</A> identifying the type as a model of Source. Typically a Source can be defined by deriving from the helper classes <A HREF="../classes/device.html#synopsis"><CODE>source</CODE></A> or <A HREF="../classes/device.html#synopsis"><CODE>wsource</CODE></A> and defining a member function <CODE>read</CODE>. |
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64 | |
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65 | <H2>Refinement of</H2> |
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66 | |
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67 | <P><A HREF="device.html">Device</A>.</P> |
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68 | |
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69 | <A NAME="types"></A> |
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70 | <H2>Associated Types</H2> |
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71 | |
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72 | <P>Same as <A HREF="device.html#types">Device</A>, with the following additional requirements:</P> |
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73 | |
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74 | <TABLE CELLPADDING="5" BORDER="1"> |
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75 | <TR><TD>Category</TD><TD>A type convertible to <A HREF="../guide/traits.html#category_tags"><CODE>device_tag</CODE></A> and to <A HREF="../guide/modes.html#mode_tags"><CODE>input</CODE></A></TD></TR> |
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76 | </TABLE> |
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77 | |
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78 | <A NAME="notation"></A> |
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79 | <H2>Notation</H2> |
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80 | |
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81 | <TABLE CELLPADDING="2"> |
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82 | <TR><TD><CODE>S</CODE></TD><TD>- A type which is a model of Source</TD></TR> |
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83 | <TR><TD><CODE>Ch</CODE></TD><TD>- The character type</TD></TR> |
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84 | <TR><TD><CODE>src</CODE></TD><TD>- Object of type <CODE>S</CODE></TD></TR> |
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85 | <TR><TD><CODE>s</CODE></TD><TD>- Object of type <CODE>Ch*</CODE></SPAN></TD></TR> |
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86 | <TR><TD><CODE>n</CODE></TD><TD>- Object of type <CODE>std::streamsize</CODE></TD></TR> |
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87 | <TR><TD><CODE>io</CODE></TD><TD>- Alias for namespace <CODE>boost::iostreams</CODE></TD></TR> |
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88 | </TABLE> |
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89 | |
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90 | <A NAME="expressions"></A> |
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91 | <H2>Valid Expressions / Semantics</H2> |
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92 | |
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93 | <TABLE CELLPADDING="5" BORDER="1"> |
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94 | <TR><TH>Expression</TH><TH>Expression Type</TH><TH>Category Precondition</TH><TH>Semantics</TH></TR> |
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95 | <TR> |
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96 | <TD> |
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97 | <PRE CLASS="plain_code"><CODE>typename <A HREF="../guide/traits.html#char_type_of_ref">char_type_of</A><S>::type</CODE></PRE> |
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98 | </TD> |
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99 | <TD><CODE>typename</CODE> of the character type</TD> |
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100 | <TD ALIGN="center">-</TD><TD ALIGN="center">-</TD> |
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101 | </TR> |
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102 | <TR> |
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103 | <TD> |
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104 | <PRE CLASS="plain_code"><CODE>typename <A HREF="../guide/traits.html#category_ref">category_of</A><S>::type</CODE></PRE> |
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105 | </TD> |
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106 | <TD><CODE>typename</CODE> of the category</TD> |
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107 | <TD ALIGN="center">-</TD><TD ALIGN="center">-</TD> |
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108 | </TR> |
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109 | <TR> |
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110 | <TD><PRE CLASS="plain_code"><CODE><A HREF="../functions/read.html">io::read</A>(src, s, n)</CODE></PRE></TD> |
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111 | <TD><CODE>std::streamsize</CODE></TD> |
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112 | <TD>Not convertible to <A HREF="direct.html"><CODE>direct_tag</CODE></A></TD> |
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113 | <TD> |
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114 | Reads up to <CODE>n</CODE> characters from the input sequence controlled by <CODE>dev</CODE> into <CODE>s</CODE>, returning the number of characters read, or <CODE>-1</CODE> to indicate end-of-sequence |
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115 | </TD> |
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116 | </TR> |
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117 | <TR> |
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118 | <TD><PRE CLASS="plain_code"><CODE>src.input_sequence()</CODE></PRE></TD> |
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119 | <TD><PRE CLASS="plain_code"><CODE>std::pair<Ch*,Ch*></CODE></PRE></TD> |
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120 | <TD>Convertible to <A HREF="direct.html"><CODE>direct_tag</CODE></A></TD> |
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121 | <TD>Returns a pair of pointers delimiting the sequence controlled by <CODE>src</CODE></TD> |
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122 | </TR> |
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123 | </TABLE> |
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124 | |
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125 | <H2>Exceptions</H2> |
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126 | |
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127 | <P> |
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128 | Errors which occur during the execution of member functions <CODE>read</CODE> or <CODE>input_sequence</CODE> are indicated by throwing exceptions. Reaching the end of the sequence is not an error. |
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129 | </P> |
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130 | |
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131 | <P> |
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132 | After an exception is thrown, a Source must be in a consistent state; further i/o operations may throw exceptions but must have well-defined behaviour. |
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133 | </P> |
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134 | |
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135 | <H2>Models</H2> |
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136 | |
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137 | <UL> |
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138 | <LI>Standard input streams and stream buffers. |
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139 | <LI><A HREF="../classes/array.html#array_source"><CODE>array_source</CODE></A>, <A HREF="../classes/file.html#file_source"><CODE>file_source</CODE></A>, <A HREF="../classes/file_descriptor.html#file_descriptor_source"><CODE>file_descriptor_source</CODE></A>, <A HREF="../classes/mapped_file.html#mapped_file_source"><CODE>mapped_file_source</CODE></A>. |
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140 | </UL> |
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141 | |
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142 | <!-- Begin Footer --> |
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143 | |
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144 | <HR> |
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145 | <P CLASS="copyright">Revised |
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146 | <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan --> |
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147 | 20 May, 2004 |
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148 | <!--webbot bot="Timestamp" endspan i-checksum="38504" --> |
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149 | </P> |
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150 | |
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151 | <P CLASS="copyright">© Copyright <A HREF="http://www.kangaroologic.com" TARGET="_top">Jonathan Turkanis</A>, 2004</P> |
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152 | <P CLASS="copyright"> |
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153 | Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <A HREF="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>) |
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154 | </P> |
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155 | |
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156 | <!-- End Footer --> |
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157 | |
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158 | </BODY> |
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