当变量从内存在C ++中删除？ [英] When are variables removed from memory in C++?

问题描述

我一直使用C ++了一点吧。我只是从来没有肯定的内存管理是如何工作的，所以这里有云：

I've been using C++ for a bit now. I'm just never sure how the memory management works, so here it goes:

我首先不确定的内存是如何在一个未分配的功能，例如：

I'm first of all unsure how memory is unallocated in a function, ex:

int addTwo(int num)
{
    int temp = 2;
    num += temp;
    return num;
}

因此​​，在这个例子中，将温度从存储器函数结束后删除？如果没有，这是怎么完成的。在C＃中，一旦其范围使用一个变量被删除。是否有其他之情况下，我应该知道的？

So in this example, would temp be removed from memory after the function ends? If not, how is this done. In C# a variable gets removed once its scope is used up. Are there also any other cases I should know about?

感谢

推荐答案

局部变量温度是在功能和开始时的堆栈上推，杀出堆栈当函数退出。

The local variable temp is "pushed" on a stack at the beginning of the function and "popped" of the stack when the function exits.

下面是从非优化的版本拆卸：

Here's a disassembly from a non optimized version:

int addTwo(int num)
{
00411380  push        ebp  
00411381  mov         ebp,esp             //Store current stack pointer
00411383  sub         esp,0CCh            //Reserve space on stack for locals etc
00411389  push        ebx  
0041138A  push        esi  
0041138B  push        edi  
0041138C  lea         edi,[ebp-0CCh] 
00411392  mov         ecx,33h 
00411397  mov         eax,0CCCCCCCCh 
0041139C  rep stos    dword ptr es:[edi] 
    int temp = 2;
0041139E  mov         dword ptr [temp],2 
    num += temp;
004113A5  mov         eax,dword ptr [num] 
004113A8  add         eax,dword ptr [temp] 
004113AB  mov         dword ptr [num],eax 
    return num;
004113AE  mov         eax,dword ptr [num] 
}
004113B1  pop         edi  
004113B2  pop         esi  
004113B3  pop         ebx  
004113B4  mov         esp,ebp                 //Restore stack pointer
004113B6  pop         ebp  
004113B7  ret

推和杀出的条款内容只是作为一个比喻。正如你可以从汇编输出看一下编译器从堆栈指针减去一个合适的值保留局部变量等一气呵成的所有内存。

The terms "pushed" and "popped" are merely meant as an analogy. As you can see from the assembly output the compiler reserves all memory for local variables etc in one go by subtracting a suitable value from the stack pointer.

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