C++ 隐含了 this，以及它是如何被压入堆栈的 [英] The C++ implicit this, and exactly how it is pushed on the stack

问题描述

我需要知道，当调用 C++ 中的类方法时，隐式this"指针是第一个参数还是最后一个参数.即:是先入栈还是最后入栈.

I need to know whether, when a class method in C++ is called, the implicit 'this' pointer is the first argument, or the last. i.e: whether it is pushed onto the stack first or last.

换句话说，我在问一个被调用的类方法是否被编译器认为是:

In other words, I'm asking whether a class method, being called, is taken by the compiler to be:

int foo::bar(foo *const this, int arg1, int arg2); 
//or:
int foo::bar(int arg1, int arg2, foo *const this);

因此，通过扩展，更重要的是，这也将回答 G++ 是否会分别最后或第一个推送 this 指针.我询问了谷歌，但我没有找到太多.

By extension therefore, and more importantly, that would also answer whether G++ would push the this pointer last or first, respectively. I interrogated google, but I didn't find much.

附带说明一下，当调用 C++ 函数时，它们的作用与 C 函数相同吗?即:

And as a side note, when C++ functions are called, do they do the same thing as C functions? i.e:

push ebp
mov ebp, esp

总而言之:被调用的类方法会像这样吗?

All in all: would a class method being called look like this?

; About to call foo::bar.
push dword 0xDEADBEEF
push dword 0x2BADBABE
push dword 0x2454ABCD ; This one is the this ptr for the example.
; this code example would match up if the this ptr is the first argument.
call _ZN3foo3barEpjj

谢谢，非常感谢.

澄清一下，我使用的是 GCC/G++ 4.3

to clarify things, I'm using GCC/G++ 4.3

推荐答案

这取决于编译器的调用约定和目标架构.

This depends on the calling convention of your compiler and the target architecture.

默认情况下，Visual C++ 不会将其压入堆栈.对于 x86，编译器将默认使用thiscall"调用约定，并将 this 在 ecx 寄存器中传递.如果为成员函数指定 __stdcall，它将作为第一个参数压入堆栈.

By default, Visual C++ will not push this on the stack. For x86, the compiler will default to "thiscall" calling convention and will pass this in the ecx register. If you specify __stdcall for you member function, it will be pushed on the stack as the first parameter.

对于 VC++ 上的 x64，前四个参数在寄存器中传递.这是第一个参数，传入rcx寄存器.

For x64 on VC++, the first four parameters are passed in registers. This is the first parameter and passed in the rcx register.

几年前，Raymond Chen 有一个关于调用约定的系列.以下是 x86 和 x64 篇文章.

Raymond Chen had a series some years ago on calling conventions. Here are the x86 and x64 articles.

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