Introducing Linking

The compiler outputs an object file for each compilation unit. In the previous example, we had three .cpp files and the compiler produced three object files. The task of the linker is to combine these object files together into a single object file. Combining files together results in relative address changes; for example, if the linker puts the rect.o file after main.o, the starting address of rect.o becomes 0x04 instead of the previous value of 0x00:

code: 
  0x00 main
  0x01 Rect r; 
  0x02 _Rect_init_(&r, 3.1, 4.05); 
  0x03 printf("%d\n", _Rect_get_area(&r)); 
  0x04 _Rect_init_ 
  0x05 side1_ = s1 
  0x06 side2_ = s2 
  0x07 return 
  0x08 _Rect_get_area_ 
  0x09 register = side1_ 
  0x0A reg_multiply side2_ 
  0x0B return 
information (symbol table):
  main: 0x00
  _Rect_init_: 0x04
  printf: ????
  _Rect_get_area_: 0x08 
  _Rect_init_: 0x04
  _Rect_get_area_...