I've just bought a new laptop for me on the travel, then on my free time, I've started to test MinGW on it by trying to compile my own OS that is written in C++, then I've created all the files needed and the kernel.cpp:

extern "C" void _main(struct multiboot_data* mbd, unsigned int magic);

void _main( struct multiboot_data* mbd, unsigned int magic )
{
   char * boot_loader_name =(char*) ((long*)mbd)[16];

   /* Print a letter to screen to see everything is working: */
   unsigned char *videoram = (unsigned char *) 0xb8000;
   videoram[0] = 65; /* character 'A' */
   videoram[1] = 0x07; /* forground, background color. */
}

And tried to compile it with g++

G:> g++ -o C:\kernel.o -c kernel.cpp -Wall -Wextra -Werror -nostdlib -nostartfiles -nodefaultlibs
kernel.cpp: In function `void _main(multiboot_data*, unsigned int)':
kernel.cpp:8: warning: unused variable 'boot_loader_name'
kernel.cpp: At global scope:
kernel.cpp:4: warning: unused parameter 'magic'

G:>

But it don't create any binary file at C:/, what can I do?