sys-file-reader: Avoid hanging forever if a system file has no variables.

[pspp] / doc / dev / system-file-format.texi

diff --git a/doc/dev/system-file-format.texi b/doc/dev/system-file-format.texi
index 0f0940b58f88a2bfe9d13c0678dc52343be14982..4eb061580db5878b467fdbf4f6608f61d114972b 100644 (file)
--- a/doc/dev/system-file-format.texi
+++ b/doc/dev/system-file-format.texi
@@ -178,7 +178,7 @@ contribute to this value beyond the first 255 bytes.   Further, system
 files written by some systems set this value to -1.  In general, it is
 unsafe for systems reading system files to rely upon this value.
 
-@item int32 compressed;
+@item int32 compression;
 Set to 0 if the data in the file is not compressed, 1 if the data is
 compressed with simple bytecode compression, 2 if the data is ZLIB
 compressed.  This field has value 2 if and only if @code{rec_type} is
@@ -262,6 +262,10 @@ wider than 255 bytes.  Such very long string variables are represented
 by a number of narrower string variables.  @xref{Very Long String
 Record}, for details.
 
+A system file should contain at least one variable and thus at least
+one variable record, but system files have been observed in the wild
+without any variables (thus, no data either).
+
 @example
 int32               rec_type;
 int32               type;
@@ -352,6 +356,7 @@ in the range.  When a range plus a value are present, the third
 element denotes the additional discrete missing value.
 @end table
 
+@anchor{System File Output Formats}
 The @code{print} and @code{write} members of sysfile_variable are output
 formats coded into @code{int32} types.  The least-significant byte
 of the @code{int32} represents the number of decimal places, and the