Initializing an variable matrix in a structure C

Question

I am having trouble with initializing a variable matrix in a structure in C. Have been reading a couple of posts(post) but I cant seem to fix it. Don't ask me why but for an assignment I need to initialize a matrix located in a structure.

My code for the struct is:

typedef struct maze{
    int row;
    int column;
    char matrix[row][column];
}maze;

By calling a different function, after reading a certain file, I need to initialize a matrix by its given parameters, so 2 parameters "row" and "column".

My code for the init function is:

struct maze* init_maze(int row, int column) {

    struct maze mazeFilled;
    struct maze *mazePointer;

    mazeFilled.row = row;
    mazeFilled.column = column;

    return mazePointer;
}

But as you can guess this is not working, people already mentioned that it is hard to create a matrix from 2 variables. Could anyone explain what I am doing wrong.

EDIT 1:

I changed my code according to the posts the struct however remains the same. I needed to allocate the pointer so it even stays active outside the scoop.

My new code for the init funct is:

struct maze* init_maze(void) {

    int row = 6;
    int column = 10;
    struct maze *mazePointer = malloc(sizeof (*mazePointer));

    mazePointer->row = row;
    mazePointer->column = column;

    return mazePointer;
}   

EDIT 2:

Think I discoverd what my error was, I did not allocate memory for the matrix. My new init function:

struct maze* init_maze(void) {

int row = 6;
int column = 10;

maze *mazePointer;
mazePointer = malloc(sizeof(maze));
mazePointer->row = row;
mazePointer->column = column;
mazePointer->matrix =  malloc(row * sizeof(char*));

for (int i; i < row; i++) {
    for(int j; j < column; j++) {
    mazePointer -> matrix[i][j] = malloc(1 * sizeof(char*));
    }
}

return mazePointer;

}

I am still not sure how to allocate the memory for just the first array, [i]. Could anyone tell me if I am in the right direction?

Answer 1

Could anyone explain what I am doing wrong?

You are returning a pointer to a local/automatic storage duration structure which is not guaranteed to exist beyond the scope { } of the function.

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There are a number of ways to do this. The aim is return a structure which remains alive and active even after returning from the function.

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The more commonly used way to do this is to allocate the structure dynamically, populate it and return a pointer to it.

struct maze* init_maze(int row, int column) 
{

    struct maze *pmazeFilled = malloc(sizeof(*pmazeFilled));

    pmazeFilled->row = row;
    pmazeFilled ->column = column;

    return pmazeFilled;
}

Remember the caller must free the allocated memory by calling free on the returned pointer.