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<H1> A.10.7 Input-Output of Characters and Strings</H1>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> For an item of type
Character the following procedures are provided: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Get(File : <B>in</B> File_Type; Item : <B>out</B> Character);<BR>
<B>procedure</B> Get(Item : <B>out</B> Character);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="CodeIndented">After skipping any line terminators and any
page terminators, reads the next character from the specified input file
and returns the value of this character in the out parameter Item.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">The exception
End_Error is propagated if an attempt is made to skip a file terminator.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Put(File : <B>in</B> File_Type; Item : <B>in</B> Character);<BR>
<B>procedure</B> Put(Item : <B>in</B> Character);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">If the line length
of the specified output file is bounded (that is, does not have the conventional
value zero), and the current column number exceeds it, has the effect
of calling New_Line with a spacing of one. Then, or otherwise, outputs
the given character to the file.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Look_Ahead (File : <B>in</B> File_Type;<BR>
Item : <B>out</B> Character;<BR>
End_Of_Line : <B>out</B> Boolean);<BR>
<B>procedure</B> Look_Ahead (Item : <B>out</B> Character;<BR>
End_Of_Line : <B>out</B> Boolean);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8/1</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">Mode_Error is
propagated if the mode of the file is not In_File. Sets End_Of_Line to
True if at end of line, including if at end of page or at end of file;
in each of these cases the value of Item is not specified. <A NAME="I6147"></A>Otherwise
End_Of_Line is set to False and Item is set to <S>the </S>the next character
(without consuming it) from the file.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Get_Immediate(File : <B>in</B> File_Type;<BR>
Item : <B>out</B> Character);<BR>
<B>procedure</B> Get_Immediate(Item : <B>out</B> Character);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">Reads the next
character, either control or graphic, from the specified File or the
default input file. Mode_Error is propagated if the mode of the file
is not In_File. End_Error is propagated if at the end of the file. The
current column, line and page numbers for the file are not affected.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Get_Immediate(File : <B>in</B> File_Type;<BR>
Item : <B>out</B> Character;<BR>
Available : <B>out</B> Boolean);<BR>
<B>procedure</B> Get_Immediate(Item : <B>out</B> Character;<BR>
Available : <B>out</B> Boolean);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">If a character,
either control or graphic, is available from the specified File or the
default input file, then the character is read; Available is True and
Item contains the value of this character. If a character is not available,
then Available is False and the value of Item is not specified. <A NAME="I6148"></A>Mode_Error
is propagated if the mode of the file is not In_File. End_Error is propagated
if at the end of the file. The current column, line and page numbers
for the file are not affected.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> For an item of
type String the following procedures are provided: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Get(File : <B>in</B> File_Type; Item : <B>out</B> String);<BR>
<B>procedure</B> Get(Item : <B>out</B> String);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>15</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">Determines the
length of the given string and attempts that number of Get operations
for successive characters of the string (in particular, no operation
is performed if the string is null).</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Put(File : <B>in</B> File_Type; Item : <B>in</B> String);<BR>
<B>procedure</B> Put(Item : <B>in</B> String);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>17</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">Determines the
length of the given string and attempts that number of Put operations
for successive characters of the string (in particular, no operation
is performed if the string is null).</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>18</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Get_Line(File : <B>in</B> File_Type;<BR>
Item : <B>out</B> String;<BR>
Last : <B>out</B> Natural);<BR>
<B>procedure</B> Get_Line(Item : <B>out</B> String; Last : <B>out</B> Natural);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>19</FONT></DIV>
<DIV Class="CodeIndented">Reads successive characters from the specified
input file and assigns them to successive characters of the specified
string. Reading stops if the end of the string is met. Reading also stops
if the end of the line is met before meeting the end of the string; in
this case Skip_Line is (in effect) called with a spacing of 1. <A NAME="I6149"></A>The
values of characters not assigned are not specified.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>20</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">If characters
are read, returns in Last the index value such that Item(Last) is the
last character assigned (the index of the first character assigned is
Item'First). If no characters are read, returns in Last an index value
that is one less than Item'First. The exception End_Error is propagated
if an attempt is made to skip a file terminator.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>21</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Put_Line(File : <B>in</B> File_Type; Item : <B>in</B> String);<BR>
<B>procedure</B> Put_Line(Item : <B>in</B> String);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>22</FONT></DIV>
<DIV Class="CodeIndented">Calls the procedure Put for the given string,
and then the procedure New_Line with a spacing of one. </DIV>
<H4 ALIGN=CENTER>Implementation Advice</H4>
<DIV Class="Paranum"><FONT SIZE=-2>23</FONT></DIV>
<DIV Class="Normal"> The Get_Immediate procedures should be implemented
with unbuffered input. For a device such as a keyboard, input should
be ``available'' if a key has already been typed, whereas for a disk
file, input should always be available except at end of file. For a file
associated with a keyboard-like device, any line-editing features of
the underlying operating system should be disabled during the execution
of Get_Immediate. </DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>24</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>26 Get_Immediate can be used
to read a single key from the keyboard ``immediately''; that is, without
waiting for an end of line. In a call of Get_Immediate without the parameter
Available, the caller will wait until a character is available.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>25</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>27 In a literal string parameter
of Put, the enclosing string bracket characters are not output. Each
doubled string bracket character in the enclosed string is output as
a single string bracket character, as a consequence of the rule for string
literals (see <A HREF="AA-2-6.html">2.6</A>).</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>26</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>28 A string read by Get or
written by Put can extend over several lines. An implementation is allowed
to assume that certain external files do not contain page terminators,
in which case Get_Line and Skip_Line can return as soon as a line terminator
is read. </FONT></DIV>
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