编译器错误：在malloc期间从类型'void *'分配给'struct'时出现不兼容的类型

Question

EDIT -- can the down voter explain? I have a clear question, with supporting evidence, and proof of prior investigation. I would like to understand why you are down voting me...?

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I am getting this error when I compile with gcc:

error: incompatible types when assigning to type 'struct cell' from type 'void *

The problem lines are:

    struct cell* cells = NULL;
    cells = malloc(sizeof(struct cell) * length);
    for (i = 0; i < length; i++) {
            cells[i] = malloc(sizeof(struct cell) * width);

I believe I have followed the proper protocol, as described here and also here . What am I missing?

Answer 1

For a multidimensional array, you want an array of type struct cell** cells :

struct cell** cells = NULL;
cells = malloc(sizeof(struct cell*) * length);
for(int i = 0; i < length; i++) {
  cells[i] = malloc(sizeof(struct cell)*width);
}

Now cells is a multidimensional array, where the first index range is the length and the second index range is the width.

Answer 2

malloc() always returns a pointer of type void * you need to type cast

To allocate memory for single element:

struct cell* new = (struct cell*) malloc(sizeof(struct cell)); //This will allocate memory and new is pointer

To access data members :

new->member_name = value; //dot(.) operator doesn't work as new is a pointer and not an identifier

To allocate memory for array :

struct cell* base = (struct cell*) malloc(sizeof(struct cell) * length); //This will allocate memory and base is base of array

To access data members :

base[i].member_name = value; //When accessing elements of array the -> operator doesn't work.