% Copyright The Numerical Algorithms Group Limited 1992-94. All rights reserved.
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The \spadtype{File(S)} domain provides a basic interface to read and
write values of type \spad{S} in files.
\xtc{
Before working with a file, it must be made accessible to \Language{} with
the \spadfunFrom{open}{File} operation.
}{
\spadpaste{ifile:File List Integer:=open("/tmp/jazz1","output")  \bound{ifile}}
}
The \spadfunFrom{open}{File} function arguments are a \spadtype{FileName}
and a \spadtype{String} specifying the mode.
If a full pathname is not specified, the current default directory is
assumed.
The mode must be one of \spad{"input"} or \spad{"output"}.
If it is not specified, \spad{"input"} is assumed.
Once the file has been opened, you can read or write data.
\xtc{
The operations \spadfunFromX{read}{File} and \spadfunFromX{write}{File} are
provided.
}{
\spadpaste{write!(ifile, [-1,2,3])        \free{ifile}\bound{ifile1}}
}
\xtc{
}{
\spadpaste{write!(ifile, [10,-10,0,111])  \free{ifile1}\bound{ifile2}}
}
\xtc{
}{
\spadpaste{write!(ifile, [7])             \free{ifile2}\bound{ifile3}}
}
\xtc{
You can change from writing to reading (or vice versa)
by reopening a file.
}{
\spadpaste{reopen!(ifile, "input")        \free{ifile3}\bound{ifile4}}
}
\xtc{
}{
\spadpaste{read! ifile                    \free{ifile4}\bound{ifile5}}
}
\xtc{
}{
\spadpaste{read! ifile                    \free{ifile5}\bound{ifile6}}
}
\xtc{
The \spadfunFromX{read}{File} operation can cause an error if one tries to
read more data than is in the file.
To guard against this possibility the \spadfunFromX{readIfCan}{File}
operation should be used.
}{
\spadpaste{readIfCan! ifile  \free{ifile6}\bound{ifile7}}
}
\xtc{
}{
\spadpaste{readIfCan! ifile  \free{ifile7}\bound{ifile8}}
}
\xtc{
You can find the current mode of the file, and the file's name.
}{
\spadpaste{iomode ifile           \free{ifile}}
}
\xtc{
}{
\spadpaste{name ifile             \free{ifile}}
}
\xtc{
When you are finished with a file, you should close it.
}{
\spadpaste{close! ifile           \free{ifile}\bound{ifileA}}
}
\noOutputXtc{
}{
\spadpaste{)system rm /tmp/jazz1  \free{ifileA}}
}
%\xtc{
%}{
%\spadcommand{)clear all  \free{}\bound{}}
%}

A limitation of the underlying LISP system is that not all values can be
represented in a file.
In particular, delayed values containing compiled functions cannot be
saved.

For more information on related topics, see
\downlink{`TextFile'}{TextFileXmpPage}\ignore{TextFile},
\downlink{`KeyedAccessFile'}{KeyedAccessFileXmpPage}\ignore{KeyedAccessFile},
\downlink{`Library'}{LibraryXmpPage}\ignore{Library}, and
\downlink{`FileName'}{FileNameXmpPage}\ignore{FileName}.
\showBlurb{File}
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