#include <iostream>
#include <stdio.h>
using namespace std;
struct DexHeader{
int off;
};
int main()
{
struct DexHeader dexHeader;
dexHeader.off = 3;
const DexHeader* lpDexHeader = &dexHeader;
//此處發生一次淺拷貝
DexHeader currentDexHeader = *lpDexHeader;
printf("0x%x\n",(unsigned long long)lpDexHeader);
printf("0x%x\n",(unsigned long long)¤tDexHeader);
//純粹的去掉const屬性
printf("0x%x\n",const_cast<DexHeader*>(lpDexHeader));
return 0;
}
結果
0x172975a0
0x172975b0
0x172975a0
const_cast用來丟棄變量的const聲明，但不能改變變量所指向的對象的const屬性。即：const_cast用於原本非const的對象；如果用於原本const的對象，結果不可預知（C++語言未對此種情況進行規定）
例子：
#include <iostream>
using namespace std;
int main()
{
const int a = 5; //主要是這裏是const,在數據區
const int * p = &a; //這裏指向的實際是棧的一個新變量
int *p_var = NULL;
p_var = const_cast <int*>(p); //強轉爲非const指針
cout << a <<endl;
*p_var = 10; //重新賦值
cout << "*p=" << *p << endl; //輸出10
cout << "*p_var=" << *p_var << endl; //輸出10
cout << "a=" << a << endl; //輸出5
system("pause");
return 0;
}
結果：
5
*p=10
*p_var=10
a=5
彙編代碼：
.text:004114C0
.text:004114C0
.text:004114C0 ; Attributes: bp-based frame
.text:004114C0
.text:004114C0 ; int __cdecl main()
.text:004114C0 _main proc near
.text:004114C0
.text:004114C0 var_E4= byte ptr -0E4h
.text:004114C0 p_var= dword ptr -20h
.text:004114C0 p= dword ptr -14h
.text:004114C0 a= dword ptr -8
.text:004114C0
.text:004114C0 push ebp
.text:004114C1 mov ebp, esp
.text:004114C3 sub esp, 0E4h
.text:004114C9 push ebx
.text:004114CA push esi
.text:004114CB push edi
.text:004114CC lea edi, [ebp+var_E4]
.text:004114D2 mov ecx, 39h
.text:004114D7 mov eax, 0CCCCCCCCh
.text:004114DC rep stosd
.text:004114DE mov [ebp+a], 5
.text:004114E5 lea eax, [ebp+a]
.text:004114E8 mov [ebp+p], eax
.text:004114EB mov [ebp+p_var], 0
.text:004114F2 mov eax, [ebp+p]
.text:004114F5 mov [ebp+p_var], eax
.text:004114F8 mov esi, esp
.text:004114FA mov eax, ds:__imp_?endl@std@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@1@AAV21@@Z ; std::endl(std::basic_ostream<char,std::char_traits<char>> &)
.text:004114FF push eax
.text:00411500 mov edi, esp
.text:00411502 push 5
.text:00411504 mov ecx, ds:__imp_?cout@std@@3V?$basic_ostream@DU?$char_traits@D@std@@@[email protected] ; std::basic_ostream<char,std::char_traits<char>> std::cout
.text:0041150A call ds:__imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QAEAAV01@H@Z ; std::basic_ostream<char,std::char_traits<char>>::operator<<(int)
.text:00411510 cmp edi, esp
.text:00411512 call j___RTC_CheckEsp
.text:00411517 mov ecx, eax
.text:00411519 call ds:__imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QAEAAV01@P6AAAV01@AAV01@@Z@Z ; std::basic_ostream<char,std::char_traits<char>>::operator<<(std::basic_ostream<char,std::char_traits<char>> & (*)(std::basic_ostream<char,std::char_traits<char>> &))
.text:0041151F cmp esi, esp
.text:00411521 call j___RTC_CheckEsp
.text:00411526 mov eax, [ebp+p_var]
.text:00411529 mov dword ptr [eax], 0Ah
.text:0041152F mov esi, esp
.text:00411531 mov eax, ds:__imp_?endl@std@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@1@AAV21@@Z ; std::endl(std::basic_ostream<char,std::char_traits<char>> &)
.text:00411536 push eax
.text:00411537 mov edi, esp
.text:00411539 mov ecx, [ebp+p]
.text:0041153C mov edx, [ecx]
.text:0041153E push edx
.text:0041153F push offset _Val ; "*p="
.text:00411544 mov eax, ds:__imp_?cout@std@@3V?$basic_ostream@DU?$char_traits@D@std@@@[email protected] ; std::basic_ostream<char,std::char_traits<char>> std::cout
.text:00411549 push eax ; _Ostr
.text:0041154A call j_??$?6U?$char_traits@D@std@@@std@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@0@AAV10@PBD@Z ; std::operator<<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,char const *)
.text:0041154F add esp, 8
.text:00411552 mov ecx, eax
.text:00411554 call ds:__imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QAEAAV01@H@Z ; std::basic_ostream<char,std::char_traits<char>>::operator<<(int)
.text:0041155A cmp edi, esp
.text:0041155C call j___RTC_CheckEsp
.text:00411561 mov ecx, eax
.text:00411563 call ds:__imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QAEAAV01@P6AAAV01@AAV01@@Z@Z ; std::basic_ostream<char,std::char_traits<char>>::operator<<(std::basic_ostream<char,std::char_traits<char>> & (*)(std::basic_ostream<char,std::char_traits<char>> &))
.text:00411569 cmp esi, esp
.text:0041156B call j___RTC_CheckEsp
.text:00411570 mov esi, esp
.text:00411572 mov eax, ds:__imp_?endl@std@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@1@AAV21@@Z ; std::endl(std::basic_ostream<char,std::char_traits<char>> &)
.text:00411577 push eax
.text:00411578 mov edi, esp
.text:0041157A mov ecx, [ebp+p_var]
.text:0041157D mov edx, [ecx]
.text:0041157F push edx
.text:00411580 push offset aPVar ; "*p_var="
.text:00411585 mov eax, ds:__imp_?cout@std@@3V?$basic_ostream@DU?$char_traits@D@std@@@[email protected] ; std::basic_ostream<char,std::char_traits<char>> std::cout
.text:0041158A push eax ; _Ostr
.text:0041158B call j_??$?6U?$char_traits@D@std@@@std@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@0@AAV10@PBD@Z ; std::operator<<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,char const *)
.text:00411590 add esp, 8
.text:00411593 mov ecx, eax
.text:00411595 call ds:__imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QAEAAV01@H@Z ; std::basic_ostream<char,std::char_traits<char>>::operator<<(int)
.text:0041159B cmp edi, esp
.text:0041159D call j___RTC_CheckEsp
.text:004115A2 mov ecx, eax
.text:004115A4 call ds:__imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QAEAAV01@P6AAAV01@AAV01@@Z@Z ; std::basic_ostream<char,std::char_traits<char>>::operator<<(std::basic_ostream<char,std::char_traits<char>> & (*)(std::basic_ostream<char,std::char_traits<char>> &))
.text:004115AA cmp esi, esp
.text:004115AC call j___RTC_CheckEsp
.text:004115B1 mov esi, esp
.text:004115B3 mov eax, ds:__imp_?endl@std@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@1@AAV21@@Z ; std::endl(std::basic_ostream<char,std::char_traits<char>> &)
.text:004115B8 push eax
.text:004115B9 mov edi, esp
.text:004115BB push 5
.text:004115BD push offset aA ; "a="
.text:004115C2 mov ecx, ds:__imp_?cout@std@@3V?$basic_ostream@DU?$char_traits@D@std@@@[email protected] ; std::basic_ostream<char,std::char_traits<char>> std::cout
.text:004115C8 push ecx ; _Ostr
.text:004115C9 call j_??$?6U?$char_traits@D@std@@@std@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@0@AAV10@PBD@Z ; std::operator<<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,char const *)
.text:004115CE add esp, 8
.text:004115D1 mov ecx, eax
.text:004115D3 call ds:__imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QAEAAV01@H@Z ; std::basic_ostream<char,std::char_traits<char>>::operator<<(int)
.text:004115D9 cmp edi, esp
.text:004115DB call j___RTC_CheckEsp
.text:004115E0 mov ecx, eax
.text:004115E2 call ds:__imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QAEAAV01@P6AAAV01@AAV01@@Z@Z ; std::basic_ostream<char,std::char_traits<char>>::operator<<(std::basic_ostream<char,std::char_traits<char>> & (*)(std::basic_ostream<char,std::char_traits<char>> &))
.text:004115E8 cmp esi, esp
.text:004115EA call j___RTC_CheckEsp
.text:004115EF mov esi, esp
.text:004115F1 push offset Command ; "pause"
.text:004115F6 call ds:__imp__system
.text:004115FC add esp, 4
.text:004115FF cmp esi, esp
.text:00411601 call j___RTC_CheckEsp
.text:00411606 xor eax, eax
.text:00411608 push edx
.text:00411609 mov ecx, ebp ; frame
.text:0041160B push eax
.text:0041160C lea edx, v ; v
.text:00411612 call j_@_RTC_CheckStackVars@8 ; _RTC_CheckStackVars(x,x)
.text:00411617 pop eax
.text:00411618 pop edx
.text:00411619 pop edi
.text:0041161A pop esi
.text:0041161B pop ebx
.text:0041161C add esp, 0E4h
.text:00411622 cmp ebp, esp
.text:00411624 call j___RTC_CheckEsp
.text:00411629 mov esp, ebp
.text:0041162B pop ebp
.text:0041162C retn
