共享内存中的C struct成员指针（mmap）

Question

I have two processes that access the same shared memory. However I want to store a dynamically allocated array in shared memory. I know this can be achieved using flexible array members but I am not allowed to use them.

I am able to allocate and access the dynamic array from the server but whenever my client attempts to access it I get a segfault. I can access other structure members just fine nontheless. Here is the logic of my code. I allocated some extra space at the end of the shared memory segment and set the array to point to the end of the segment.

struct A{
    int a;
    struct B *other;
}
struct B{
    int b;
}
...
//Server
fd=shm_open("shared", O_CREAT | O_RDWR, 0666);
ftruncate(fd, sizeof(struct A)+200*sizeof(struct B));
struct A *ptr=mmap(NULL, sizeof(struct A)+200*sizeof(struct B), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
ptr->other=(struct B *)(ptr+1);       
int i=0;
for(i=0;i<200;i++){
    struct B b;
    ptr->other[i]=b;
}
...
//Client
int fd=shm_open("shared", O_RDWR, 0666);
struct A *ptr=mmap(NULL, sizeof(struct A)+200*sizeof(struct B), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
printf("%i", ptr->other[0]);// SEGFAULT

Any help would be appreciated!

Answer 1

The solution was to define the other list outside the structure

struct A{
    int a;
}
struct B{
    int b;
}
...
//Server
fd=shm_open("shared", O_CREAT | O_RDWR, 0666);
ftruncate(fd, sizeof(struct A)+200*sizeof(struct B));
struct A *ptr=mmap(NULL, sizeof(struct A)+200*sizeof(struct B), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
struct B *other=(struct B *)(ptr+1);      
int i=0;
for(i=0;i<200;i++){
    struct B b;
    other[i]=b;
}
...
//Client
int fd=shm_open("shared", O_RDWR, 0666);
struct A *ptr=mmap(NULL, sizeof(struct A)+200*sizeof(struct B), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
struct B *other=(struct B *)(ptr+1); 
printf("%i", other[0]);