51单片机KEIL编译错误*** WARNING L1: UNRESOLVED EXTERNAL SYMBOL
    SYMBOL:  TIME_FLAG
    MODULE:  .listmain.obj (MAIN)
*** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL
    SYMBOL:  TIME_FLAG
    MODULE:  .listmain.obj (MAIN)
    ADDRESS: 03F6H
*** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL
    SYMBOL:  TIME_FLAG
    MODULE:  .listmain.obj (MAIN)
    ADDRESS: 03F9H
*** WARNING L1: UNRESOLVED EXTERNAL SYMBOL
    SYMBOL:  TIME_FLAG
    MODULE:  .listinterrupt.obj (INTERRUPT)
*** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL
    SYMBOL:  TIME_FLAG
    MODULE:  .listinterrupt.obj (INTERRUPT)
    ADDRESS: 079BH
Program Size: data=14.0 xdata=33 code=1954   FLAG_TIME是1毫秒中断标志位，check_time检测等待时间，都在头文件里定义了的，还是有警告extern bit Time_FLAG;         //10ms 时间标记  extern bit Time_FLAG;         //10ms 时间标记
extern unsigned char aa;
//extern long temp2,temp;         //10ms 时间标记
extern unsigned char Check_time;          //检测时间