13. End-of-file rules

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:

assigning 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);
executing a return statement;
executing the special `yyterminate()' action;
or, switching to a new buffer using `yy_switch_to_buffer()' as shown in the example above.

<<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

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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