How can I have a dynamically allocated 2D array in

问题:

This question already has an answer here:

• How do I correctly set up, access, and free a multidimensional array in C? 5 answers

So I have a program with a struct

typedef struct s_struct {
    int rows;
    int cols;
    char* two_d; //This is supposed to be the 2D array
} *GRID; 

I want to create a struck and dynamically allocate memory to it and then fill the 2D array but I don't know how. Here is what I have for the create(int prows, int pcols) function:

GRID grid = malloc(sizeof(struct s_struct));
grid ->rows = prows;
grid ->cols = pcols;
grid ->two_d = malloc(sizeof(char) * (rows*cols));

I don't understand how this creates a 2D array if it even does and how I can go about filling the array.

回答1:

this line:

grid ->two_d = malloc(sizeof(char) * (rows*cols));

allocates a 'continuous in memory' grid/matrix that can be referenced by:

grid[row_offset][cols_offset]

where the 'row_offset' can be 0...(row-1)

where the 'cols_offset' can be 0...(cols-1)

note: 'sizeof(char)' is always 1, 
so including that phrase
in the malloc parameter just clutters the code 
because '(1*something)' is always 'something' 
as the 1 has no effect.

suggest: remove the 'sizeof(char)' from the malloc parameter