Complicated when compiling in c++ but not in c (gcc)

I have problem with multiply declaration in c++, but not in c. You could see code for more information.

file main.c

#ifndef VAR
#define VAR
int var;
#endif
int main(){}

file other.c

#ifndef VAR
#define VAR
int var;
#endif

Compile with gcc

gcc main.c other.c
>> success

Compile with g++

g++ main.c other.c
Output:
/tmp/ccbd0ACf.o:(.bss+0x0): multiple definition of `var'
/tmp/cc8dweC0.o:(.bss+0x0): first defined here
collect2: ld returned 1 exit status

My gcc and g++ version:

gcc --version
gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3
Copyright (C) 2011 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

g++ --version
g++ (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3
Copyright (C) 2011 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.