c - lexical analysis stops after yy_scan_string() is finished -

i use flex make lexical analyzer. want analyse define compiler statements in form: #define identifier identifier_string. keep list of (identifier identifier_string) pair. when reach in file identifier #define list need switch lexical analysis main file analyse corresponding identifier_string. (i don't put complete flex code because big) here's part:

{identifier}                    {   // search if identifier in list                                     if( p = get_identifier_string(yytext) )                                     {                                         puts("define matched");                                         yypush_buffer_state(yy_scan_string(p));                                     }                                     else//if not in list print identifier                                     {                                         printf("identifier %s\n",yytext);                                     }                                 } <<eof>>                         {                                     puts("eof reached");                                     yypop_buffer_state();                                     if ( !yy_current_buffer )                                     {                                         yyterminate();                                     }                                     loop_detection = 0;                                 } 

the analysis of identifier_string executes fine. when eof reached want switch @ initial buffer , resume analysis. finishes printing eof reached.

although approach seems logical, won't work because yy_scan_string replaces current buffer, , happens before call yypush_buffer_state. consequently, original buffer lost, , when yypop_buffer_state called, restored buffer state (now terminated) string buffer.

so need little hack: first, duplicate current buffer state onto stack, , switch new string buffer:

/* was: yypush_buffer_state(yy_scan_string(p)); */ yypush_buffer_state(yy_current_buffer); yy_scan_string(p);