http://fossies.org/dox/glibc-2.18/strcpy_8c_source.html

strcpy.c

#include <stddef.h>
#include <string.h>
#include <memcopy.h>

#undef strcpy

/* Copy SRC to DEST.  */
char *
strcpy (dest, src)
     char *dest;
     const char *src;
{
  char c;
  char *s = (char *) src;
  const ptrdiff_t off = dest - s - 1;

  do
    {
      c = *s++;
      s[off] = c;
    }
  while (c != '\0');

  return dest;
}