如何在malloc内存中初始化非POD数据 [英] How to initialize non-POD data in malloc memory

问题描述

我有一个结构，其中以std :: list作为其数据成员.该std :: list是std :: pair的集合.

I have a structure which has an std::list as its data member. That std::list is an collection of std::pair.

赞这个(.h文件内)

extern struct_info tt;
typedef struct_s *struct_info;
typedef 
struct struct_s {
  std::list < std::pair <char*, int> > names;
};

我正在为.cpp文件中的该结构分配内存，如下:

I am allocating memory for this structure in my .cpp file as:

tt = mem_malloc(sizeof(struct_t));

mem_malloc是我自己的内存分配例程.请注意，它已经在.h文件中设为外部.

mem_malloc is my own memory allocating routine. Please note that it is already made extern in .h file.

稍后，当我尝试使用以下代码将任何元素推回列表中时:

Later, when I try to push_back any element into the list with following code:

std::pair <char*, int> myPair = std:make_pair("A", 5);
(tt->names).push_back(myPair);

执行push_back时会崩溃.我不知道这里发生了什么.我是否需要为struct_s构造函数中的列表调用任何构造函数或初始化程序?

It crashes while doing push_back. I do not know what is happening here. Do I need to call any constructor or initializer for the list in struct_s constructor?

你们怎么看?

推荐答案

您不能只分配大小为 sizeof(struct_t)的内存，并希望能够像使用<这里存在code> struct_t 实例-您需要首先构造它.例如

You can't just allocate memory with size sizeof(struct_t) and expect to be able to use that memory as if a struct_t instance existed there - you need to construct it first. E.g.

tt = mem_malloc(sizeof(struct_t));
new (tt) struct_s{}; // <- "placement `new`"

// use `tt`...

tt->~struct_s(); // <- explicit destructor call
// deallocate tt

但是，这是一个糟糕的主意，尤其是如果手动完成.标准库提供了分配器支持-您应该创建一个可以与标准库无缝使用的分配器.

This is however a terrible idea, especially if done manually. The Standard Library provides allocator support - you should create an allocator that can be seamlessly used with the Standard Library instead.

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