C Windows-内存映射文件-共享结构中的动态数组 [英] C Windows - Memory Mapped File - dynamic array within a shared struct

问题描述

我正在尝试共享类似于以下示例的结构:

typedef struct { 
    int *a; 
    int b; 
    int c;
} example;

我正在尝试在进程之间共享此结构，我发现的问题是，当我使用malloc初始化'a'时，将无法从第二个进程内访问该数组. 是否可以将此动态数组添加到内存映射文件中?

解决方案

您可以将其设置为

typedef struct { 
    int b; 
    int c;
    int asize; // size of "a" in bytes - not a number of elements
    int a[0];
} example;

/* allocation of variable */
#define ASIZE   (10*sizeof(int))
example * val = (example*)malloc(sizeof(example) + ASIZE);
val->asize = ASIZE;

/* accessing "a" elements */
val->a[9] = 125;

技巧是在结构的末尾将大小为a的数组设为零，然后将malloc的大小乘以结构的大小再加上a的实际大小.

您可以将此结构复制到映射文件.您应该复制sizeof(example)+val->asize个字节.另一方面，只需读取asize，您就会知道应该读取多少数据-因此，读取sizeof(example)字节，realloc字节并读取其他的asize字节.

I'm trying to share a struct similar to the following example:

typedef struct { 
    int *a; 
    int b; 
    int c;
} example;

I'm trying to share this struct between processes, the problem that I find is that when I initialize 'a' with malloc, I won't be able to access the array from within the second process. Is it possible to add this dynamic array to the memory mapped file?

解决方案

You can have it as

typedef struct { 
    int b; 
    int c;
    int asize; // size of "a" in bytes - not a number of elements
    int a[0];
} example;

/* allocation of variable */
#define ASIZE   (10*sizeof(int))
example * val = (example*)malloc(sizeof(example) + ASIZE);
val->asize = ASIZE;

/* accessing "a" elements */
val->a[9] = 125;

the trick is zero sized a array at the end of the structure and malloc larger then size of structure by actual size of a.

You can copy this structure to mmapped file. You should copy sizeof(example)+val->asize bytes. On the other side, just read asize and you know how many data you should read - so read sizeof(example) bytes, realloc and read additional asize bytes.

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