Linker error : no definition for "DATA"(variable of type struct data_t)

[youssef.amimi]

I have declared a typedef struct data_t on my jsmn.h

after that I declared a variable DATA of type data_t on jsmn.c

and i defined N,T,C and H

then i declared DATA of type Data_t as extern on ScreenViewBase.cpp

and i try to display DATA.N on the screen

but a linker error appear : no definition for DATA referenced from ScreenViewBase.o

PS1: I do the same with time : in ScreenViewBase.cpp I declared extern RTC_TimeTypeDef sTime then  I write Unicode::snprintf(Ndata, 6, "%02d",sTime.Hours ); and it work perfectly.

PS2: I work with stm32f769 and with IAR 8.32.3

[Tesla DeLorean]

Check symbols in .MAP file see in you have multiple instances of DATA variable.

C++ name mangling likely the driver here.