C++声明细问# Programming - 葵花宝典
m*o
1 楼
class C{ virtual void proc (int x) {...}..};
..
C obj;
C* ptr;
..
obj.proc(5); //(1)
ptr->proc(5); //(2)
请问1和2的却别，2要比1多执行几步机器指令？
..
C obj;
C* ptr;
..
obj.proc(5); //(1)
ptr->proc(5); //(2)
请问1和2的却别，2要比1多执行几步机器指令？
g*n
2 楼
For obj.proc(5):
1. calculat the address of obj, and push this address onto the stack (or
load it into a registary). Member function requires "this" pointer.
2. push 5 onto the stack (or load it into a registary).
3. call C::proc(int). Assuming compiler is smart enough to de-virtual the
call to proc.
For ptr->proc(5):
1. push the value of ptr onto the stack (or load it into a registary).
2. push 5 onto the stack (or load it into a registary).
3. get the enry address from vtable.
4. call C::proc
1. calculat the address of obj, and push this address onto the stack (or
load it into a registary). Member function requires "this" pointer.
2. push 5 onto the stack (or load it into a registary).
3. call C::proc(int). Assuming compiler is smart enough to de-virtual the
call to proc.
For ptr->proc(5):
1. push the value of ptr onto the stack (or load it into a registary).
2. push 5 onto the stack (or load it into a registary).
3. get the enry address from vtable.
4. call C::proc
m*o
3 楼
哥们真牛，以后去做QUANT DEVELOPER吧，最高年薪100万
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