初始化指向struct的指针数组的正确方法是什么？

Question

I am trying to implement trie data structure:-

typedef struct tries{
    char university[20];
    struct tries *path[10];
} tries;

tries* head = (tries*)malloc(sizeof(tries));
head->path = { NULL } ;

whenever I try to initialize all the elements of path array to NULL I am getting this error:-

clang -fsanitize=signed-integer-overflow -fsanitize=undefined -ggdb3 -O0 -std=c11 -Wall -Werror -Wextra -Wno-sign-compare -Wshadow    tries.c  -lcrypt -lcs50 -lm -o tries
tries.c:20:18: error: expected expression
    head->path = { NULL } ;
                 ^
1 error generated.
make: *** [tries] Error 1

how can I initialize all path array's elements to NULL
I am using this NULL value in my Insert and Search functions.

void Search(char* university, char* year, tries* head){
    int pos = 0;
    int length = strlen(year);
    tries* temp = head;

    for(int i = 0 ; i < length ; i++){
        pos = (int) (year[i]%48);

        if(temp->path[pos] != NULL){
            temp = temp->path[pos];
        } else {
            printf("%s Not Found !!\n", university);
            return;
        }

    }

    if(strcmp(temp->university, university) == 0){
        printf("%s is Presnt.\n", university);
    } else {
        printf("%s Not Found !\n", university);
    }

}

Answer 1

Just use calloc() instead of malloc() and you'll get all 0 s in the the char -array and all NULL s into the pointer-array.

Change

tries * head = (tries*)malloc(sizeof(tries));

to be

tries * head = (tries*)calloc(1, sizeof(tries));

Also please note that

• there is no need to cast void -pointer in C
• sizeof is an operator not a function

so just do:

tries * head = calloc(1, sizeof (tries));

And if you want this code line to be more robust, surviving the change of the type head points to make it

tries * head = calloc(1, sizeof *head);

---

As you are dealing with struct s which in fact are assignable you could do the following:

const tries init_try = {0};

...

  tries * head = malloc(sizeof *head);
  if (NULL == head)
    exit(EXIT_FAILURE);
  *head = init_try;