flex中的yyrestart怎么用?

如题,我需要在main.c中使用yyrestart和yyparse,但编译会警告implicit declaration of function ‘yyrestart’ [-Wimplicit-function-declaration]
我include了syntax.tab.h,还要怎么做才能不警告?

http://www.cppblog.com/woaidongmao/archive/2008/11/23/67637.html