Initialize structure C via function

Question

Therefore, I need to write a type data structure vectorin C. In general, I created this structure:

struct Vector
{
    int length;
    int *elements;
};

And functions like these:

void initialize_vector(struct Vector* vector);
void create_vector(struct Vector* vector, int* array, int n);
void remove_vector(struct Vector* vector);
void vector_add_element(struct Vector* vector, int element);
void vector_insert(struct Vector* vector, int index, int element);
void vector_remove_element(struct Vector* vector, int element);
void vector_remove_at(struct Vector* vector, int index);

Now, a function initialize_vector(), I just wanted to initialize the attributes of the default vectors (for example, from lengthto 0 *elementsto NULL). I wrote something like this:

void initialize_vector(struct Vector* vector)
{
    vector->elements = NULL;
    vector->length = 0;
}

And I tried to check if it works, so I wrote this piece of code:

#include <stdio.h>
#include "vector.h"


int main(int arc, char** argv)
{
    struct Vector* vec;
    initialize_vector(vec);
    printf("%d\n", vec->length);
    return 0;
}

I got famous Segmentation fault, so I checked the GDB, and, of course, when all fastens this line: vector->elements = NULL;.

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Answer 1

, . , undefined .

struct Vector :

struct Vector vec;
initialize_vector(&vec);
printf("%d\n", vec.length);

struct Vector , malloc :

struct Vector *initialize_vector()
{
    struct Vector *vector = malloc(sizeof(*vector));
    if (!vector) {
        perror("malloc failed");
        exit(1);
    }
    vector->elements = NULL;
    vector->length = 0;
    return vector;
}

...

struct Vector *vector = initialize_vector();

Answer 2

dbush , . C-, .

struct Vector * vec;

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