为嵌套结构指针分配内存 [英] Allocating memory for nested structure pointer

问题描述

我正在使用C代码生成器来创建具有以下结构的头文件:

I am using a C code generator that is creating header files with following structures:

typdef struct Place {   
    struct Forest {
        int trees;
    } *Forest;
} Place ;

并在c ++项目中使用它们.

And using them in a c++ project.

当我尝试访问Place.Forest->树时，我遇到了段错误，因为Place.Forest是一个悬空的指针.

When I try to access Place.Forest->trees, I get a segfault because Place.Forest is a dangling pointer.

我无法正确分配它，因为 Place.Forest = malloc(sizeof(Place.Forest)); 只会返回指针的大小.

I can't properly malloc it because Place.Forest = malloc(sizeof(Place.Forest)); will just return the size of the pointer.

我不能使用 Place.Forest=malloc(sizeof(struct Forest)); 因为我正在从C ++访问Place，并且范围限制使我无法看到Forest.

I can't use Place.Forest=malloc(sizeof(struct Forest)); Because I am accessing Place from C++ and scoping prevents me from being able to see Forest.

如何在不更改位置或取消嵌套森林的情况下为森林分配内存?

How do I allocate memory for Forest without changing Place or un-nesting Forest?

由于要自动生成大量代码，因此无法修改结构.

Modifying the structures is impracticable due to the large amount of code that is being automatically generated.

推荐答案

经过几个小时的摸索，我找到了解决方案.

After several hours of screwing around, I found a solution.

您必须使用extern C来使编译器使用C样式链接，但还必须使用C ++的作用域分辨率::来正确解析结构类型.

You have to use extern C to get the compiler to use C style linking, but you also have to use C++'s scope resolution :: to correctly resolve the structure type.

头文件:

#ifdef __cplusplus
extern "C" {
#endif

typdef struct Place {   
    struct Forest {
        int trees;
    } *Forest;
} Place ;

#ifdef __cplusplus
}
#endif

程序:

#include <stdlib.h>
#include <iostream>
extern "C" {      
    static void allocateForest(Place *p){
        p->Forest = (struct Place::Forest *)malloc(sizeof(struct Place::Forest));
    }
}

int main(void){
    Place p;
    allocateForest(&p);
    p.Forest->trees = 1;
    std::cout << p.Forest->trees << std::endl;
    return 0;
}

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