keil C编译出现很多这种警告怎么解决啊？？？function "Gpio_Set" declared implicitly

source\App_Rtc8025.c(32): warning:  #223-D: function "I2CWrite" declared implicitly
source\App_Rtc8025.c(46): warning:  #223-D: function "I2CRead" declared implicitly
compiling App_24lc256.c...
source\App_24lc256.c(34): warning:  #223-D: function "Gpio_Clr" declared implicitly
source\App_24lc256.c(37): warning:  #223-D: function "printf" declared implicitly
source\App_24lc256.c(40): warning:  #223-D: function "printf" declared implicitly
source\App_24lc256.c(40): warning:  #870-D: invalid multibyte character sequence
source\App_24lc256.c(40): warning:  #870-D: invalid multibyte character sequence
source\App_24lc256.c(41): warning:  #223-D: function "I2CWrite" declared implicitly
有很多让人看着很不爽，不知道怎么去掉这些警告！
期盼高手解答！！

应该是没有包含相应的头文件导致的

source\App_24lc256.c(40): warning:  #870-D: invalid multibyte character sequence
这条警告怎么关啊

我也忘记了，不过不影响程序运行！

搜了搜，好像是有全角字符引起的，你查查看！！！