CHAPTER 51. C++ CHAPTER 51. C++
; _this$ = ecx
push ebp
mov ebp, esp
push ecx
mov DWORD PTR _this$[ebp], ecx
mov eax, DWORD PTR _this$[ebp]
mov ecx, DWORD PTR _a$[ebp]
mov DWORD PTR [eax], ecx
mov edx, DWORD PTR _this$[ebp]
mov eax, DWORD PTR _b$[ebp]
mov DWORD PTR [edx+4], eax
mov eax, DWORD PTR _this$[ebp]
mov esp, ebp
pop ebp
ret 8
??0c@@QAE@HH@Z ENDP ; c::c
The constructors are just functions, they use a pointer to the structure inECX, copying the pointer into their own local
variable, however, it is not necessary.
From the C++ standard [ISO13, p. 12.1] we know that constructors are not required to return any values. In fact, internally,
the constructors return a pointer to the newly created object, i.e.,this.
Now thedump()method:
Listing 51.3: MSVC_this$ = -4 ; size = 4
?dump@c@@QAEXXZ PROC ; c::dump, COMDAT
; _this$ = ecx
push ebp
mov ebp, esp
push ecx
mov DWORD PTR _this$[ebp], ecx
mov eax, DWORD PTR _this$[ebp]
mov ecx, DWORD PTR [eax+4]
push ecx
mov edx, DWORD PTR _this$[ebp]
mov eax, DWORD PTR [edx]
push eax
push OFFSET ??_C@_07NJBDCIEC@?$CFd?$DL?5?$CFd?6?$AA@
call _printf
add esp, 12
mov esp, ebp
pop ebp
ret 0
?dump@c@@QAEXXZ ENDP ; c::dump
Simple enough:dump()takes a pointer to the structure that contains the twoint’s fromECX, takes both values from it and
passes them toprintf().
The code is much shorter if compiled with optimizations (/Ox):
Listing 51.4: MSVC??0c@@QAE@XZ PROC ; c::c, COMDAT
; _this$ = ecx
mov eax, ecx
mov DWORD PTR [eax], 667
mov DWORD PTR [eax+4], 999
ret 0
??0c@@QAE@XZ ENDP ; c::c
_a$ = 8 ; size = 4
_b$ = 12 ; size = 4
??0c@@QAE@HH@Z PROC ; c::c, COMDAT
; _this$ = ecx
mov edx, DWORD PTR _b$[esp-4]
mov eax, ecx
mov ecx, DWORD PTR _a$[esp-4]
mov DWORD PTR [eax], ecx
mov DWORD PTR [eax+4], edx