Multiple definition of ... linker error

Question

I defined a special file: config.h

My project also has files:

t.c, t.h pp.c, pp.h b.c b.h l.cpp 

and #includes:

in t.c:

    #include "t.h"     #include "b.h"     #include "pp.h"     #include "config.h" 

in b.c:

    #include "b.h"     #include "pp.h" 

in pp.c:

    #include "pp.h"     #include "config.h" 

in l.cpp:

    #include "pp.h"     #include "t.h"     #include "config.h" 

there are no include directives in my *.h files, only in *.c files. I defined this in config.h:

const char *names[i] =         {             "brian", "stefan", "steve"         }; 

and need that array in l.cpp, t.c, pp.c but Im getting this error:

pp.o:(.data+0x0): multiple definition of `names' l.o:(.data+0x0): first defined here t.o:(.data+0x0): multiple definition of `names' l.o:(.data+0x0): first defined here collect2: ld returned 1 exit status make: *** [link] Error 1 

I have include guards in every *.h file I use in my project. Any help solving this?

Answer 1

Don't define variables in headers. Put declarations in header and definitions in one of the .c files.

In config.h

extern const char *names[]; 

In some .c file:

const char *names[] = {    "brian", "stefan", "steve" }; 

If you put a definition of a global variable in a header file, then this definition will go to every .c file that includes this header, and you will get multiple definition error because a varible may be declared multiple times but can be defined only once.

Also, one more thing you can do if you have to define your variables inside of a header file you can use the static keyword.

static const char *names[] = {   "brian", "stefan", "steve" }; 

This way variable names will be defined only once in your entire program and can be accessed multiple number of times.