C语言struct数组

Question

In my program, I have to create structs, in my case, I have struct Processor here is my example:

struct Processor{
    int id;
    struct Task **task;
}

In the main I create set of processors (2 processors for example), and I have to add in tasks in each processor using this function struct Processor * create_processor(int id, struct Task **task );

Here is the function:

struct Processor * create_processor(int id, struct Task **task){
    struct Processor * pr = (struct Processor *) (malloc(sizeof(struct Processor)));
    pr->id = id;
    //how to initialize Task set??
    return pr;
}

Now how to initialize the set of tasks in the function? and how to use elements of taskset? I used processor[1]->task[1]->id = 5; but it returns ERROR Segmentation fault (core dumped)

Help please

Answer 1

When you do

struct Processor * pr = (struct Processor *) (malloc(sizeof(struct Processor)));

you've now initialized an empty Processor struct. Since the task member of the struct is a pointer (actually a double-pointer) all you have in your freshly initialized Processor is equivalent to: struct Processor { id: 0, task: 0 } , ie it just contains a null pointer for the task member. That's probably why you get Segmentation fault , which is the type of error that occurs when your program accesses uninitialized memory.

You'll also have to malloc an array of Task* (task pointers) for however many tasks each processor has to have. Eg

pr.task = (struct Task **) malloc(sizeof(struct Task *) * N_TASKS);  // pr.task should probably be called pr.tasks??

then you also need to initialize memory for each actual task:

for (int idx = 0; idx < N_TASKS; idx++) {
    pr.task[idx] = (struct Task *) malloc(sizeof(struct Task));
}

and so on for each Processor you want to initialize.

Answer 2

Maybe this can help. I suppose you allocate memory for tasks before calling your function. Here you have 10 tasks and I create one processor with 3 tasks:

struct Processor{
    int id;
    struct Task **task;
};

struct Task{ int id; int WCET;};

struct Processor * create_processor(int id, struct Task **task){
    struct Processor * pr = (struct Processor *) (malloc(sizeof(struct Processor)));
    pr->id = id;
    pr->task = task;
    return pr;
}


int main() {
    struct Task taskArray[10]; /* memory for 10 tasks */
    struct Task * taskPtrArray[3]; /* pointers to 3 tasks */
    taskPtrArray[0] = &taskArray[2]; /* pointer to task 2 */
    taskPtrArray[1] = &taskArray[6]; /* pointer to task 6 */
    taskPtrArray[2] = &taskArray[9]; /* pointer to task 9 */

    struct Processor * p1 = create_processor(1, taskPtrArray);

    printf("p1->id = %d \n", p1->id);
    p1->task[2]->WCET = 999;
    printf("p1->task[2]->WCET = %d \n", taskArray[9].WCET);
}

The output is:

p1->id = 1

p1->task[2]->WCET = 999

---

As "Some programmer dude" said. The function assing tasks with:

pr->task = task;