C++类的空指针调用成员函数的代码

class Student
{
private:
 int age;
public:
 Student() {}
 Student(int age) : age(age) {}
 int getAge() { return this->age; }
};
 
int main(int argc, char const *argv[])
{
 Student s(10);
 int age = s.getAge();
 
 Student* ps = new Student(10);
 age = ps->getAge();
 
 return 0;
}

int main(int argc, char const *argv[])
{
00A41860 push  ebp 
00A41861 mov   ebp,esp 
00A41863 push  0FFFFFFFFh 
00A41865 push  0A461D2h 
00A4186A mov   eax,dword ptr fs:[00000000h] 
00A41870 push  eax 
00A41871 sub   esp,104h 
00A41877 push  ebx 
00A41878 push  esi 
00A41879 push  edi 
00A4187A lea   edi,[ebp-110h] 
00A41880 mov   ecx,41h 
00A41885 mov   eax,0CCCCCCCCh 
00A4188A rep stos dword ptr es:[edi] 
00A4188C mov   eax,dword ptr [__security_cookie (0A4B004h)] 
00A41891 xor   eax,ebp 
00A41893 mov   dword ptr [ebp-10h],eax 
00A41896 push  eax 
00A41897 lea   eax,[ebp-0Ch] 
00A4189A mov   dword ptr fs:[00000000h],eax 
 Student s(10);
00A418A0 push  0Ah /*构造函数中的实参值: 10 */
00A418A2 lea   ecx,[s] /*取实例s的内存地址,并赋值给寄存器ECX*/
00A418A5 call  Student::Student (0A4103Ch) /*调用位于内存地址0A4103Ch的构造函数*/
 int age = s.getAge();
00A418AA lea   ecx,[s] /*取实例s的内存地址,并赋值给寄存器ECX*/
00A418AD call  Student::getAge (0A412D5h) /*调用位于内存地址0A412D5h的成员函数*/
00A418B2 mov   dword ptr [age],eax /*成员函数的返回值赋给变量age*/
 
 Student* ps = new Student(10);
00A418B5 push  4 /*类实例所需的内存大小,有一个int类型成员,故为4字节(32位编译)*/
00A418B7 call  operator new (0A412A3h) /*调用全局的内存分配函数,类似C的malloc函数*/
00A418BC add   esp,4 /*栈顶加4个字节,用于保存operator new内存分配返回的内存地址值*/
00A418BF mov   dword ptr [ebp-108h],eax /*eax存的就是返回的内存地址,赋值到ptr [ebp-108h]这是处于栈中的内存*/
00A418C5 mov   dword ptr [ebp-4],0 
00A418CC cmp   dword ptr [ebp-108h],0 
00A418D3 je   main+8Ah (0A418EAh) /*与上一句联动,如果分配的地址为0,即失败,跳转到0A418EAh*/
00A418D5 push  0Ah /*调用构造函数的实参值: 10*/
00A418D7 mov   ecx,dword ptr [ebp-108h] /*取指针ps指向的实例的内存地址值并赋值给寄存器ECX*/
00A418DD call  Student::Student (0A4103Ch) /*调用位于内存地址 0A4103Ch 的构造函数*/
00A418E2 mov   dword ptr [ebp-110h],eax 
00A418E8 jmp   main+94h (0A418F4h) 
00A418EA mov   dword ptr [ebp-110h],0 
00A418F4 mov   eax,dword ptr [ebp-110h] 
00A418FA mov   dword ptr [ebp-0FCh],eax 
00A41900 mov   dword ptr [ebp-4],0FFFFFFFFh 
00A41907 mov   ecx,dword ptr [ebp-0FCh] 
00A4190D mov   dword ptr [ps],ecx 
 age = ps->getAge();
00A41910 mov   ecx,dword ptr [ps] /*取实例s的内存地址值并赋值给寄存器ECX*/
00A41913 call  Student::getAge (0A412D5h) /*调用位于内存地址 0A412D5h 的成员函数*/
 age = ps->getAge();
00A41918 mov   dword ptr [age],eax 
 
 return 0;
00A4191B xor   eax,eax 
}

class Student
{
private:
 int age;
public:
 Student() {}
 Student(int age) : age(age) {}
 void eat() {}
};
 
int main(int argc, char const *argv[])
{
 Student* ps = nullptr;
 ps->eat();
 return 0;
}

#include <iostream>
using namespace std;
 
class Student
{
private:
 int age;
public:
 Student() {}
 Student(int age) : age(age) {}
 static int classtime() {
  return 9;
 }
 void eat() {}
};
 
int main(int argc, char const *argv[])
{
 Student* ps = nullptr;
 int time = ps->classtime();
 cout << time << endl;
 return 0;
}