恰好通过自由释放内存中的数据的内容（）？ [英] What happens to the data in memory deallocated by free()?

问题描述

正好是在一个内存位置present刚刚被释放的数据多么免费（）？是，数据还删除，存储现在有一个垃圾的价值？或该数据仍然存在那里，直到一个新的数据被存储在该存储器位置（将来）？

我的意思是，对于低于code：

 为int * PTR;
PTR =的malloc（sizeof的（INT））;
* PTR = 1;
 //假设PTR = 2000
 //现在免​​费
免费（PTR）;
//我的问题是什么是存储在内存中的地址2000现在的价值？
//这还算是'1'或一些垃圾值？
 

解决方案

结果是未predictable。有可能发生几个选项。问题的关键是，你不能依赖于免费发布存储器的任何行为（）

一些例子：

• 的内存可以不变（保持不变，因为它是使用相同的数据）。


• 它可以给另一个存储器分配，在这种情况下，它可以在任何时候被覆盖。


• 可以归零。


• 包含内存页面可以被返回到操作系统，从进程的内存映射删除它，使你的程序崩溃，如果您尝试访问它。

What happens to the data that is present in a memory location that has just been freed by a free() ? Is that data also deleted and the memory will now have a garbage value ? Or that data still persists there untill a new data is stored in that memory location (in future) ?

I mean, for code below:

int *ptr;
ptr = malloc(sizeof(int));
*ptr = 1;
 // Suppose ptr = 2000
 //Free now
free(ptr);
// My question is what is the value stored in memory address 2000 now ?
// Is it still '1' or some garbage value ?

解决方案

The result is unpredictable. There are several options that can happen. The point is that you cannot rely on any behavior of the memory released by free()

Some examples:

• the memory can be untouched (remain the same as it is with the same data).
• It can be given to another memory allocation, in which case it can be written over at any point.
• It can be zeroed.
• The page containing the memory can be returned to the OS, removing it from the memory map of your process, making your program crash if you try to access it.

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