更改局部变量的地址 [英] Changing the address of a local variable

问题描述

我想使用 xor算法交换两个局部变量，但是它不允许我更改变量的地址.如果我创建了指向变量的指针，它将允许它，但是不使用指针就可以做到这一点吗?

I want to swap two local variables using the xor algorithm, however it will not allow me to change the address of the variables. If I create pointers to the variables, it will allow it, but is it possible to do this without using pointers?

我正在尝试这样做

Point a = Point();
Point b = Point(1,1);

&a ^= &b;
&b ^= &a;
&a ^= &b;

这是我最想实现的目标

Point a = Point();
Point b = Point(1,1);

Point *a_ptr = &a;
Point *b_ptr = &b;

a_ptr = (Point *)(((unsigned long)a_ptr) ^ (unsigned long)b_ptr);
b_ptr = (Point *)(((unsigned long)a_ptr) ^ (unsigned long)b_ptr);
b_ptr = (Point *)(((unsigned long)a_ptr) ^ (unsigned long)b_ptr);

// The pointers are switched, but this will not work
&a = a_ptr;

推荐答案

C语言变量在运行时不像高级语言中的变量那样存在.对于编译器，局部变量"a"表示堆栈帧的地址-2"或任何其他值.该引用仅在编译时存在，并由声明固定.在运行时，生成的代码仅从硬编码的地址获取.因此，使用代码将变量指向不同的位置会尝试更改不存在的内容.

C language variables don't exist at runtime like variables in higher-level languages. Local variable "a" means, to the compiler, "the address of the stack frame - 2", or whatever it is. This reference exists only at compile time, and is fixed by the declaration. At runtime, the generated code simply fetches from the hard-coded address. So making the variable point to a different place with code is trying to change something that doesn't exist.

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