Thread: multiple include of header file gives compile errors

Hi All

I need some guidance with header files because I can't solve the following compile error:

Code:

make
gcc -I./lib  -c file1.c  -o file1.o
gcc -I./lib  -c file2.c  -o file2.o
gcc -I./lib  -c file.c  -o file.o
gcc -Wall -g -fast -o stats file1.o file2.o file.o -L./lib -lmyconfig 
ld: duplicate symbol _default_keys in file.o and file1.o
collect2: ld returned 1 exit status
make: *** [stats] Error 1

Both file.c and file1.c include libmyconfig.h and file.c includes file1.h.
libmyconfig.h looks (simplyfied) like

Code:

void check_config_file(char *file) ;
int load_config_file(char *filename) ;
struct CONFIG
 {
    int  *var1 ;
    char *var2 ;
 } ;
char *default_keys[]   =  {"var1", "var2"} ;
char *default_values[] =  {"10", "20"} ;

So, default_keys is included twice. I tried to solve this by adding ifndef .... endif:

Code:

#ifndef BLA
#define BLA
.....
#endif

Unfortunately it didn't change anything Any suggestions why?

Because those two lines don't belong in a header file. If all these other files need to know about that variable, then you should put "extern char * default_keys[]" in the header, and one file needs to define them.

Ok, make sense!, but then I have one last question, if I have a header file like

Code:

void check_config_file(char *file) ;
int load_config_file(char *filename) ;
struct CONFIG
 {
    int  *var1 ;
    char *var2 ;
 } ;

why would one use #ifndef FOO ..... #endif, because it will not give compile errors!

check, thnx