Why the simple code doesn't compile?

Here is the code:

Code:

#include <stdio.h>

extern end;
extern edata;
extern etext;

int I;

main(int argc, char **argv)
{

  int i;
  int *ii;

  printf("&etext = 0x%lx\n", &etext);
  printf("&edata = 0x%lx\n", &edata);
  printf("&end   = 0x%lx\n", &end);

  printf("\n");
  ii = (int *) malloc(sizeof(int));

  printf("main   = 0x%lx\n", main);
  printf("&I     = 0x%lx\n", &I);
  printf("&i     = 0x%lx\n", &i);
  printf("&argc  = 0x%lx\n", &argc);
  printf("&ii    = 0x%lx\n", &ii);
  printf("ii     = 0x%lx\n", ii);

}

But the compiler complains:

Code:

g++ -c -g main.cc -o main.o 
main.cc:22: error: ISO C++ forbids declaration of `end' with no type
main.cc:23: error: ISO C++ forbids declaration of `edata' with no type
main.cc:24: error: ISO C++ forbids declaration of `etext' with no type

"extern" is not a data type. You need "extern int" or "extern void*" or whatever.

In fact I don't see why you need extern at all.

Indeed, you'll just get linker errors that way.

Also, are you aware that you're writing C code but posting in the C++ board?

It's compiled using C++, though, so main must return int or you'll get another error.