Help! Flex++ option yyclass?

[cylin]

Dear all,

To compile with g++, I got
" no int MyLexer::yylex() member function declared in class MyLexer".
What  should I  write in MyLexer::yylex()?

In my lex file, I use
%option c++
%option yyclass="MyLexer"

Here is MyLexer.h
#ifndef _MyLexer_h_
#define _MyLexer_h_

#include <fstream.h>
#include <FlexLexer.h>

class MyLexer: public yyFlexLexer {
public:
  MyLexer(istream* poStream):yyFlexLexer(poStream) {}
  ~MyLexer() {}
public:
  int A;
  char* B;
};
#endif

Please help, thx.
Regards,
cylin.