why Multiple define error ...

hi,

i have created a header file with guard and it looks like

somehead.h as

.
.
some #defines
.
.
const long int slim_nil = 0;
const long int SLIM_INT_MIN = (-2147483647-1);
.
.
.

and i have included this header file in two c files and thru their corresponding header

files

say ...1.c includes 1.h which includes somehead.h and
...2.c includes 2.h which includes somehead.h, now while i compiling these 1.c and 2.c file
together in gcc i receive error as

/tmp/cciaeWli.o(.rodata+0x0): multiple definition of `slim_nil'
/tmp/cc0QuOGU.o(.rodata+0x0): first defined here
/tmp/cciaeWli.o(.rodata+0x4): multiple definition of `SLIM_INT_MIN'
/tmp/cc0QuOGU.o(.rodata+0x4): first defined here
/tmp/cciaeWli.o(.rodata+0x8): multiple definition of `SLIM_INT_MAX'

but here i wonder, why it is not saying multiple defines for the #defines
whats wrong!

Sorry!, if it is something silly that i dont know...

macros (created with #define) are expanded by the preprocessor doing text substitution. They never exist as symbols in an executable, so the linker has no reason to complain.

With integer definitions like;

Code:

---

const long int slim_nil = 0;

---

a const int is declared and defined. If you place that in a header file that is #include'd in multiple source files, those source files are compiled into object files and each object file has a copy. The linker sees the variable definition in multiple object files, and complains about multiple definitions.

The fix is to use;

Code:

---

extern const long int slim_nil;  /*  A declaration, not a definition */

---

in your header file. And in EXACTLY one source file in your project which #include's that header, place this somewhere AFTER the #include directive.

Code:

---

const long int slim_nil = 0;  /*  Corresponding definition */

---

Thanks grumpy ...