The special rule "<<EOF>>" indicates actions which are to be taken when an end-of-file is encountered and yywrap() returns non-zero (i.e., indicates no further files to process). The action must finish by doing one of four things:
yyin
to a new input file (in previous
versions of flex, after doing the assignment you
had to call the special action YY_NEW_FILE
; this is
no longer necessary);
return
statement;
<<EOF>> rules may not be used with other patterns; they may only be qualified with a list of start conditions. If an unqualified <<EOF>> rule is given, it applies to all start conditions which do not already have <<EOF>> actions. To specify an <<EOF>> rule for only the initial start condition, use
<INITIAL><<EOF>>
These rules are useful for catching things like unclosed comments. An example:
%x quote %% ...other rules for dealing with quotes... <quote><<EOF>> { error( "unterminated quote" ); yyterminate(); } <<EOF>> { if ( *++filelist ) yyin = fopen( *filelist, "r" ); else yyterminate(); }
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