[General] Undefined symbols in Keil

[uplifting_mind]

Hello,
I´m trying to build project with Rx and Tx interrupts from USART for STM32F10x. For Tx is used fifo buffer as a structure. During building this project, I obtained a following errors messages on the picture bellow. Notice that periph_init.h is included in both main.c and stdio_through_usart.c, where this symbols are using.
Where is a problem?

 

[RohanDey]

Have you defined these variables in your source file, or these are just extern declarations? I think you should define the variables in the source file to overcome the error.

 

[uplifting_mind]

You are right, it working. But this variables must be realy declared in both of this files? There are no directives for situation, when I want to have this declarations only in header file?

 

[RohanDey]

A variable must be defined.

You declare it as an extern variable to use it in another file.