I have a structure:

struct Path{
    int8_t maxtopy;
};

And I want to create an array of pointers to structure Path. I've tried something like that:

int main(){
    struct Path *paths[NUMBER_OF_PATHS]; 
    init_paths(paths);
}

void init_paths(struct Path **paths){
    paths[0]->maxtopy = -1;

    for(int i = 1; i < NUMBER_OF_PATHS; i  )
        paths[i]->maxtopy = -1;
}

It is not going to work. Value to the first path is assigned correctly. But when for loop starts I am gettting Segmentation fault. I already figured out that when I am creating array of pointers, only the first pointer is going to be assigned to some structure. So I cannot e.g. paths[1]->maxtopy = -1;, because paths[1] doesn't point to any existing structure.

I have tried something like this:

for(int i = 1; i < NUMBER_OF_PATHS; i  ){
        static struct Path a;
        paths[i] = &a;
        paths[i]->maxtopy = i;
}

It doesn't work because it initialize a only once. So every pointer in paths array points to the same structure.

My question is: How to create an array of pointers that point to initialized structures?

CodePudding user response：

You've created an array of pointers, butt the pointers need to point to something. You can dynamically allocate each with malloc.

struct Path{
    int8_t maxtopy;
};

int main(void) {
    struct Path *paths[NUMBER_OF_PATHS]; 

    for (size_t i = 0; i < NUMBER_OF_PATHS; i  ) {
        paths[i] = malloc(sizeof(struct Path));
        paths[i]->maxtopy = i;
    }

    return 0;
}

Of course, if your array is declared in main and is not of excessive size, you may want to simply write the following.

int main(void) {
    struct Path paths[NUMBER_OF_PATHS]; 

    for (size_t i = 0; i < NUMBER_OF_PATHS; i  ) {
        paths[i].maxtopy = i;
    }

    return 0;
}

CodePudding user response：

const int NUMBER_OF_PATHS = 10;

struct Path {
    int8_t maxtopy;
};

void init_paths(struct Path** paths) {
    for (int i = 0; i < NUMBER_OF_PATHS; i  ) {
        paths[i] = (Path*)malloc(sizeof(Path));
        paths[i]->maxtopy = i;
    }
}

int main() {
    struct Path* paths[NUMBER_OF_PATHS];

    init_paths(paths);

    for (auto i : paths) {
        printf("%d\n", i->maxtopy);
    }
}