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Static Semantics
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The procedures Get and Put for items of the type Character, String,
numeric types, and enumeration types are described in subsequent
subclauses. Features of these procedures that are common to most of
these types are described in this subclause. The Get and Put procedures
for items of type Character and String deal with individual character
values; the Get and Put procedures for numeric and enumeration types
treat the items as lexical elements.
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All procedures Get and Put have forms with a file parameter, written
first. Where this parameter is omitted, the appropriate (input or
output) current default file is understood to be specified. Each
procedure Get operates on a file of mode In_File. Each procedure Put
operates on a file of mode Out_File or Append_File.
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All procedures Get and Put maintain the current column, line, and page
numbers of the specified file: the effect of each of these procedures
upon these numbers is the result of the effects of individual transfers
of characters and of individual output or skipping of terminators. Each
transfer of a character adds one to the current column number. Each
output of a line terminator sets the current column number to one and
adds one to the current line number. Each output of a page terminator
sets the current column and line numbers to one and adds one to the
current page number. For input, each skipping of a line terminator sets
the current column number to one and adds one to the current line
number; each skipping of a page terminator sets the current column and
line numbers to one and adds one to the current page number. Similar
considerations apply to the procedures Get_Line, Put_Line, and Set_Col.
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Several Get and Put procedures, for numeric and enumeration types, have
format parameters which specify field lengths; these parameters are of
the nonnegative subtype Field of the type Integer.
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Input-output of enumeration values uses the syntax of the corresponding
lexical elements. Any Get procedure for an enumeration type begins by
skipping any leading blanks, or line or page terminators. Get procedures
for numeric or enumeration types start by skipping leading blanks, where
a blank is defined as a space or a horizontal tabulation character.
Next, characters are input only so long as the sequence input is an
initial sequence of an identifier or of a character literal (in
particular, input ceases when a line terminator is encountered). The
character or line terminator that causes input to cease remains
available for subsequent input.
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For a numeric type, the Get procedures have a format parameter called
Width. If the value given for this parameter is zero, the Get procedure
proceeds in the same manner as for enumeration types, but using the
syntax of numeric literals instead of that of enumeration literals. If a
nonzero value is given, then exactly Width characters are input, or the
characters up to a line terminator, whichever comes first; any skipped
leading blanks are included in the count. The syntax used for numeric
literals is an extended syntax that allows a leading sign (but no
intervening blanks, or line or page terminators) and that also allows
(for real types) an integer literal as well as forms that have digits
only before the point or only after the point.
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Any Put procedure, for an item of a numeric or an enumeration type,
outputs the value of the item as a numeric literal, identifier, or
character literal, as appropriate. This is preceded by leading spaces if
required by the format parameters Width or Fore (as described in later
subclauses), and then a minus sign for a negative value; for an
enumeration type, the spaces follow instead of leading. The format given
for a Put procedure is overridden if it is insufficiently wide, by using
the minimum needed width.
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Two further cases arise for Put procedures for numeric and enumeration
types, if the line length of the specified output file is bounded (that
is, if it does not have the conventional value zero). If the number of
characters to be output does not exceed the maximum line length, but is
such that they cannot fit on the current line, starting from the current
column, then (in effect) New_Line is called (with a spacing of one)
before output of the item. Otherwise, if the number of characters
exceeds the maximum line length, then the exception Layout_Error is
propagated and nothing is output.
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The exception Status_Error is propagated by any of the procedures Get,
Get_Line, Put, and Put_Line if the file to be used is not open. The
exception Mode_Error is propagated by the procedures Get and Get_Line if
the mode of the file to be used is not In_File; and by the procedures
Put and Put_Line, if the mode is not Out_File or Append_File.
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The exception End_Error is propagated by a Get procedure if an attempt
is made to skip a file terminator. The exception Data_Error is
propagated by a Get procedure if the sequence finally input is not a
lexical element corresponding to the type, in particular if no
characters were input; for this test, leading blanks are ignored; for an
item of a numeric type, when a sign is input, this rule applies to the
succeeding numeric literal. The exception Layout_Error is propagated by
a Put procedure that outputs to a parameter of type String, if the
length of the actual string is insufficient for the output of the item.
Examples
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In the examples, here and in subclauses See section A.10.8 Input-Output for Integer Types, and
See section A.10.9 Input-Output for Real Types, the string quotes and the lower case letter b are not
transferred: they are shown only to reveal the layout and spaces.
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N : Integer;
...
Get(N);
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-- Characters at input Sequence input Value of N
-- bb-12535b -12535 -12535
-- bb12_535e1b 12_535e1 125350
-- bb12_535e; 12_535e (none) Data_Error raised
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Example of overridden width parameter:
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Put(Item => -23, Width => 2); -- "-23"
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