[英]Dynamic memory allocation in C functions called from R language
I'm writing an R package that calls a C script.我正在编写一个调用 C 脚本的 R 包。 The C script uses a structure with a dynamically determined length: the length of the array forest->edges
depends on the data passed from R. C 脚本使用动态确定长度的结构:数组forest->edges
的长度取决于从 R 传递的数据。
typedef struct {
unsigned int n_edge;
...
unsigned int max_node;
unsigned int edges[];
} forest;
forest * forest_new (unsigned int *n_edge) {
forest *f = malloc(sizeof(forest) + (2 * *n_edge * sizeof(int)));
f->n_edge = *n_edge;
...
f->max_node = 0;
return f;
}
The code runs successfully in C, but crashes when an R call triggers forest_new
.代码在 C 中成功运行,但在 R 调用触发forest_new
时崩溃。 My hunch is that the crash results from memory allocation, and indeed the R manual mentions alternative means of allocating memory (eg R_alloc
, Calloc
), which threads elsewhere seems to suggest should be used in place of malloc
/ calloc
.我的直觉是从内存分配的碰撞结果,并且实际上ř手册提到分配存储器的替代手段(例如R_alloc
, Calloc
),该线程 别处似乎表明应该代替使用malloc
/ calloc
。
So part 1 of the question is when calls to malloc
/ calloc
should, or must, be replaced by R-safe equivalents (perhaps they are irrelevant to my problem?).所以问题的第 1 部分是对malloc
/ calloc
调用何时应该或必须被 R 安全等价物替换(也许它们与我的问题无关?)。 Part 2 of the question is how the R-safe functions can handle structures whose length is dynamically determined.问题的第 2 部分是 R 安全函数如何处理长度是动态确定的结构。
You can use malloc/calloc
and free
in packages to allocate and free memory, but you have to handle out of memory errors like in any C application.您可以在包中使用malloc/calloc
和free
来分配和释放内存,但您必须像在任何 C 应用程序中一样处理内存不足错误。 You can use Calloc/Free/Realloc
provided by R and then you will get the error handled in the "R way" (an R error when out of memory).您可以使用 R 提供的Calloc/Free/Realloc
,然后您将获得以“R 方式”处理的错误(内存不足时的 R 错误)。 The R_alloc
function allows you to allocate temporary data that is freed automatically when your external function exits (when you get back to R, it is stack-based allocation). R_alloc
函数允许您分配在外部函数退出时自动释放的临时数据(当您返回 R 时,它是基于堆栈的分配)。
R does not care about whether your C code uses structures with dynamically determined length (flexible arrays), R does not access your structure at all. R 不关心您的 C 代码是否使用动态确定长度的结构(灵活数组),R 根本不访问您的结构。
If you need more help please post a self-contained example or provide more information about the error.如果您需要更多帮助,请发布一个独立的示例或提供有关错误的更多信息。 Perhaps it is also worth checking n_edge
has a correct/sane value in forest_new
.或许,这也是值得一试n_edge
已经在正确的/理智值forest_new
。
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