how to use a bit variable defined in another module?

Dear Jim：
I have tried，but failed。：（
no head file is included in c program.
The head file in assem.asm is as follows：

#ifndef __MY_H__
#define    __MY_H__
－>extrn unsigned char bdata flags;
   sbit red_flag = flags^1;
#endif __MY_H__

Dear Jim：
I have tried，but failed。：（
no head file is included in c program.
The head file in assem.asm is as follows：

#ifndef __MY_H__
#define    __MY_H__
－>extrn unsigned char bdata flags;
   sbit red_flag = flags^1;
#endif __MY_H__

Oh,sorry.The extrn directive can be written like this:

//my.h
#ifndef __MY_H__
#define __MY_H__

//Declaration
#ifdef __C51__
    extrn unsigned char bdata flags;
#else
    EXTRN DATA:BYTE (flags)
#endif
sbit red_flag = flags^1;//Don't put this line to C source files

#ifdef __C51__
//C function prototype
void TextOut (BYTE byChar);
#endif //__C51__

#endif //__MY_H__

Dear Jim,
oh，my！I copied your code to my project。But it didn't work!

extrn DATA:BYTE(flags);//ILLEGAL USE OF A RESERVED WORD;
sbit red_flag = flags^1;//INAVLID SIMPLE RELOCATABLE EXPRESSION;

"See the spec please. "
Which spec?GS51.pdf?Cx51.pdf?A51.pdf?
I have read GS51.pdf.But didn't see anything about this.Let me check it again.

A51.pdf, P131

Thank you,Jim.
I am reading Cx51.pdf.I am going to that after I finish Cx51.pdf.^_^
Thank you once more.

Sorry,John.Now I have compiled it successfully.It will be right,I think.

//my.h
#ifndef __MY_H__
#define __MY_H__

//Declaration
#ifdef __A51__
    EXTRN DATA (flags)
    EXTRN BIT  (red_flag)
#else
    extern unsigned char bdata flags;
    extern bit red_flag;
#endif

#ifdef __C51__
//C function prototype
void TextOut (BYTE byChar);
#endif //__C51__

#endif //__MY_H__

//my.c
unsigned char bdata flags;
sbit red_flag = flags^1;

Dear Jim,thank you so much from China West Lake.^_^，I have compiled it successfully too。^_^Appreciate you。
Thank God，It is done。

Dear Jim:
Thank you for helping me with this problem.
Now I've got another qustion that:
in my main.c flie,I define as follows:
sbit sda = P1^1;
sbit scl = P1^2;

Now I wanna use sda & scl in my assem.asm file,how to declare them? I have tried these:
extrn bit(sda);extrn bit(scl);
but failed.:(

So is it possible?If yes,then how?
expecting your reply.

You can put them into the header file and include it in your asm files.

Dear Jim:
Thank you very much.^_^ It is done again.
and thank you once more.