(.text+0x12): undefined reference to `rpl_fprintf'

问题1：(.text+0x12): undefined reference to `rpl_fprintf'
解决办法：在yacc前面添加
%{
#undef yyerror
void yyerror (char *s);
%}
在第三部分添加：
void yyerror (char *s) {
fprintf ("%s\n", s);
}
可以解决问题，但是不能错误提示啦！
参看下面的说明之后就可以啦

5: Working around a bison bug

Normally, we'd rely on the bison run-time library to supply a main program, which would invoke the yyparse function and exit when it returned -- essentially, this code:
int main() { yyparse(); return EXIT_SUCCESS; }

To get this automatically, we'd add the -ly option at the end of the command invoking gcc to compile bison's output. As it happens, however, there is currently a bug in the bison library's implementation of the yyerror function, and gcc refuses to deal with it, issuing error messages that look like this:

/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/liby.a(yyerror.o): In function `yyerror':
(.text+0x12): undefined reference to `rpl_fprintf'
collect2: error: ld returned 1 exit status

To work around this, we'll define our own main and yyerror functions. The main we need is the one shown above. yyerror is also elementary:
int yyerror (char const *message)
{
fputs(message, stderr);
fputc('\n', stderr);
return 0;
}
这个比较好！定义为最终解决办法！
Add these function definitions at the appropriate points in your lc.y file.

参看：
http://stackoverflow.com/questions/13073780/error-while-executing-c-file-developed-using-lex-and-yacc-tools
http://pubs.opengroup.org/onlinepubs/7908799/xcu/yacc.html
http://lists.gnu.org/archive/html/help-bison/2011-11/msg00000.html