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关于c++引用机制的疑问

2010/11/15镜像同步2 回复

以下是来自一篇blog中的一个例子 #include <iostream> using namespace std; class Object { public: Object(int value1, int value2):a(value1), b(value2) {} int a; int b; }; int main() { Object o1(1,2); Object o2(3,4); cout<<o1.a<<" "<<o1.b<<" "<<o2.a<<" "<<o2.b<<endl; function(o1, o2); cout<<o1.a<<" "<<o1.b<<" "<<o2.a<<" "<<o2.b<<endl; return 0; } void function (Object& o1, Object& o2) { Object temp=o1; o1=o2; o2=temp; } #include <iostream> using namespace std; class Object { public: Object(int value1, int value2):a(value1), b(value2) {} int a; int b; }; int main() { Object o1(1,2); Object o2(3,4); cout<<o1.a<<" "<<o1.b<<" "<<o2.a<<" "<<o2.b<<endl; function(o1, o2); cout<<o1.a<<" "<<o1.b<<" "<<o2.a<<" "<<o2.b<<endl; return 0; } void function (Object& o1, Object& o2) { Object temp=o1; o1=o2; o2=temp; } 输出结果是 3 4 1 2 将函数function做如下修改 C++代码 void function (Object& o1, Object& o2) { Object& temp=o1; o1=o2; o2=temp; } void function (Object& o1, Object& o2) { Object& temp=o1; o1=o2; o2=temp; } 结果是： 3 4 3 4 以下是部分汇编代码 void function (Object& o1, Object& o2) { 00411770 push ebp 00411771 mov ebp,esp 00411773 sub esp,0CCh 00411779 push ebx 0041177A push esi 0041177B push edi 0041177C lea edi,[ebp-0CCh] 00411782 mov ecx,33h 00411787 mov eax,0CCCCCCCCh 0041178C rep stos dword ptr es:[edi] Object& temp=o1; 0041178E mov eax,dword ptr [o1] 00411791 mov dword ptr [temp],eax o1=o2; 00411794 mov eax,dword ptr [o2] 00411797 mov ecx,dword ptr [eax] 00411799 mov edx,dword ptr [eax+4] 0041179C mov eax,dword ptr [o1] 0041179F mov dword ptr [eax],ecx 004117A1 mov dword ptr [eax+4],edx o2=temp; 004117A4 mov eax,dword ptr [temp] 004117A7 mov ecx,dword ptr [eax] 004117A9 mov edx,dword ptr [eax+4] 004117AC mov eax,dword ptr [o2] 004117AF mov dword ptr [eax],ecx 004117B1 mov dword ptr [eax+4],edx } 对引用的理解是引用值（指针）->对象名（指针）->对象内存空间我的疑问在于，在汇编代码中 Object& temp=o1; 0041178E mov eax,dword ptr [o1] 00411791 mov dword ptr [temp],eax o2=temp; 004117A4 mov eax,dword ptr [temp] 004117A7 mov ecx,dword ptr [eax] 004117A9 mov edx,dword ptr [eax+4] 004117AC mov eax,dword ptr [o2] 004117AF mov dword ptr [eax],ecx 004117B1 mov dword ptr [eax+4],edx 这两部分同样是引用传值为什么 Object& temp=o1; 传递所指的是对象指针而o2=temp; 传递的是对象的值？

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