keil 编译时出现这样的错误，怎么回事？

*** ERROR L104: MULTIPLE PUBLIC DEFINITIONS
SYMBOL: TX_ADDRESS
MODULE: rf.obj (RF)
*** ERROR L104: MULTIPLE PUBLIC DEFINITIONS
SYMBOL: RX_MODE
MODULE: rf.obj (RF)
*** ERROR L104: MULTIPLE PUBLIC DEFINITIONS
SYMBOL: ?_SPI_WRITE_BUF?BYTE
MODULE: rf.obj (RF)
*** ERROR L104: MULTIPLE PUBLIC DEFINITIONS
SYMBOL: _SPI_WRITE_BUF
MODULE: rf.obj (RF)
*** ERROR L104: MULTIPLE PUBLIC DEFINITIONS
SYMBOL: ?_SPI_READ_BUF?BYTE
MODULE: rf.obj (RF)
*** ERROR L104: MULTIPLE PUBLIC DEFINITIONS
SYMBOL: _SPI_READ_BUF
MODULE: rf.obj (RF)
*** ERROR L104: MULTIPLE PUBLIC DEFINITIONS
SYMBOL: _SPI_RW
MODULE: rf.obj (RF)
*** WARNING L16: UNCALLED SEGMENT, IGNORED FOR OVERLAY PROCESS
SEGMENT: ?PR?RX_MODE?NRF24L01
*** WARNING L16: UNCALLED SEGMENT, IGNORED FOR OVERLAY PROCESS
SEGMENT: ?PR?_GETDATA?NRF24L01
*** WARNING L16: UNCALLED SEGMENT, IGNORED FOR OVERLAY PROCESS
SEGMENT: ?PR?NRF24L01_INITIAL?RF
*** WARNING L16: UNCALLED SEGMENT, IGNORED FOR OVERLAY PROCESS
SEGMENT: ?PR?NRF24L01IOCONFIG?RF
*** WARNING L16: UNCALLED SEGMENT, IGNORED FOR OVERLAY PROCESS
SEGMENT: ?PR?_SPI_READ?RF
*** WARNING L16: UNCALLED SEGMENT, IGNORED FOR OVERLAY PROCESS
SEGMENT: ?PR?TX_MODE?RF
*** WARNING L16: UNCALLED SEGMENT, IGNORED FOR OVERLAY PROCESS
SEGMENT: ?PR?REC_RF_DATA?RF
*** WARNING L1: UNRESOLVED EXTERNAL SYMBOL
SYMBOL: _DELAY_2US
MODULE: rf.obj (RF)
*** WARNING L1: UNRESOLVED EXTERNAL SYMBOL
SYMBOL: RF_SEND_BUF
MODULE: rf.obj (RF)
*** WARNING L1: UNRESOLVED EXTERNAL SYMBOL
SYMBOL: RF_REC_BUF
MODULE: rf.obj (RF)
*** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL
SYMBOL: _DELAY_2US
MODULE: rf.obj (RF)
ADDRESS: 0324H
*** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL
SYMBOL: _DELAY_2US
MODULE: rf.obj (RF)
ADDRESS: 0351H
*** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL
SYMBOL: _DELAY_2US
MODULE: rf.obj (RF)
ADDRESS: 025CH
*** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL
SYMBOL: RF_SEND_BUF
MODULE: rf.obj (RF)
ADDRESS: 026FH
*** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL
SYMBOL: RF_SEND_BUF
MODULE: rf.obj (RF)
ADDRESS: 0271H
*** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL
SYMBOL: _DELAY_2US
MODULE: rf.obj (RF)
ADDRESS: 0292H
*** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL
SYMBOL: RF_REC_BUF
MODULE: rf.obj (RF)
ADDRESS: 04F3H
*** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL
SYMBOL: RF_REC_BUF
MODULE: rf.obj (RF)
ADDRESS: 04F5H
Program Size: data=49.0 xdata=0 code=1385
目标未创建

这个问题分别是重复定义了么，怎么能是没注册呢！！！
对于比较小的程序，一般只有一个c文件和一个头文件,全局变量我们通常会直接定义在c文件中，在程序之前加int i定义。如果要在头文件中定义有以下两种方法：用extern来声明:extern int i;这一句只是对变量i进行声明，在c文件的程序之前必须加上int i进行定义。extern int i=0;这一句声明和定义都做了。
对于大一点的程序，有很多c文件和头文件，这个时候全局变量就必须在头文件中声明(不需要初始化)，然后在一个c文件中定义(该初始化的要初始化)。如果在头文件中定义，则编译的时候会出现重复定义的错误。如果只有头文件中声明就会出现没有定义有警告。
*** ERROR L104: MULTIPLE PUBLIC DEFINITIONS
SYMBOL: K
MODULE: 222.obj (222)
出现上述错误则是因为变量k重复定义，把你的头文件中的变量定义前加extern(只是变量声明不用初始化)，再在某一个你要调用该变量的c文件的程序之前再定义(注意第一个调用的c文件要负责附带初始化该变量，其他调用的c文件就不需要初始化过程啦)

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