Hello all, My project with 3 files as following ,the MAIN is in sys.c,all 3 files are compiled well each other. File a: including sys.c and common.h File b: including rtk.c and rtk.h File c: including blt.c and blt.h rtk.h: ... extern uchar code rtk_Cmd[20]={...}; extern struct Time {uchar Sec;...}; extern struct Date {...}; extern struct Time sGps; ... rtk.c: #include <rtk.h> ... syc.c: #include <common.h> #include <rtk.h> #include <blt.h> .... void main() { ... Func1(sGps.Sec); Func2(rtk_Cmd); ... } when build all files, the error L104:mutiple public defintion (rtk_cmd) Warning L1: unresolved external symbol(sGps). Give me your hands ,thanks a lot!
And now, rtk.h: struct MesInfo {...}; struct MesInfo GpsInfo; ... rtk.c: #include<rtk.h> ... Func1(GpsInfo.*); ... sys.c: #include<common.h> #include<rtk.h> void main() { ... Func2(GpsInfo.*) ... } all *.c can be compiled well. Even in the common.h has "extern struct MesInfo GpsInfo;"or not.when built all files,"error L104 :Mutiple public defintion(GpsInfo)" is show.What's the matter?
You have DECLARED GpsInfo in rtk.h Then, you include rtk.h in both rtk.c and sys.c files - therefore you have declared it twice (in both of files) - resulting in "Multiple public definition" error. - Dejan
Thank you for your help. I have resolved it as follow: rtk.h: struct MesInfo { ... } rtk.c: #include<rtk.h> struct MesInfo GpsInfo; .... sys.c: #include<rtk.h> extern struct MesInfo GpsInfo; ... In this way,all files can be build ,is it right?
In this way,all files can be build ,is it right? It may work, but it's not right. As a rule of thumb: never write 'extern' in a .c file --- it only ever should appear in .h files. In your case, this line:
extern struct MesInfo GpsInfo;
"You have DECLARED GpsInfo in rtk.h Then, you include rtk.h in both rtk.c and sys.c files - therefore you have declared it twice (in both of files) - resulting in 'Multiple public definition' error." Not quite: He has defined GpsInfo in rtk.h - resulting in 'Multiple public definition' error. The definition must be in exactly one source file; there can be as many extern declarations as you like!