c - Link error during gcc compile with makefile -

(before moving on,
the absence of frees , writing variables never used in codes,
intended testing tool)

wrote codes these , makefile this:

unread_two.h

#ifndef __unread_two_h #define __unread_two_h  const int sizeof_int = sizeof(int); int addtwo(); 

unread_twomain.c

#include <stdio.h>  #include <stdlib.h> #include "unread_two.h"  int main(int argc, char *argv[]) {     int *x;      x = (int *)malloc(sizeof_int);     x = addtwo();     free(x);      return 0; } 

unread_two.c

#include <stdio.h> #include <stdlib.h> #include <unread_two.h>  int addtwo() {     int *y, *z, sum;     y = (int *)malloc(sizeof_int);     z = (int *)malloc(sizeof_int);      *y = 3;     sum = *y + *y;     return sum; } 

makefile

cc=gcc ccflags=-g  %.o: %.c     $(cc) -c $< $(ccflags)  all: unread_two clobber: clean     rm -f *~ \#`\# core  clean:     rm -f unread_two *.o  unread_two: unread_twomain.o unread_two.o  unread_twomain.o: unread_two.h  unread_two.o: unread_two.h 

and when put make all, message appears:

unread_twomain.o:(.rodata+0x0): multiple definition of `sizeof_int' unread_two.o:(.rodata+0x0): first defined here collect2: error: ld returned 1 exit status 

what things should fix?

you shouldn't defining sizeof_int in header, otherwise you'll multiple definitions when include header in more 1 compilation unit, have seen. instead declare in header , define in source file:

// unread_two.h  extern const int sizeof_int;         // *declare* sizeof_int 

// unread_two.c  const int sizeof_int = sizeof(int);  // *define* sizeof_int 

alternatively in particular case might justified in doing "old skool" way, macro:

// unread_two.h  #define sizeof_int sizeof(int)