嵌套指向结构体的指针，指向包含结构体的指针？

Question

First, I have a struct:

typedef struct {
    int type;
    union expr value;
}lval;

and union which is defined as below to save room:

union expr{
    long num;
    char* err;
    char* sym;
    sexpr* sexpr1;
};

and in the sexpr* is

typedef struct {
    int count;
    struct lval** cell;
}sexpr;

I try to use it as below,

void lval_del(lval* v){
     lval_del(v->value.sexpr1->cell[i]); 
}

but my compiler gave me a warning:

Parameter type mismatch: Incompatible pointer types 'lval *' and 'struct anonymous::lval *'.

When I try code like below

lval* lval_add(lval* v,lval* x) {
    v->value.sexpr1->cell = realloc(v->value.sexpr1->cell, sizeof(lval*)*v->value.sexpr1->count);
    v->value.sexpr1->cell[v->value.sexpr1->count-1]=x;
    return v;
}

I get the same warning.

I ignored the warning and compiled it successfully, but when I run it, it crashes. I think it's the problem causing the warning. How can I solve it?

Edit: the full code as I compiled it is below:

typedef struct {
   int count;
   struct lval** cell;
}sexpr;

union expr{
    long num;
    char* err;
    char* sym;
    sexpr* sexpr1;
};

typedef struct {
    int type;
    union expr value;
}lval;

void lval_del(lval* v){
    switch (v->type) {
        case LVAL_NUM:
            break;
        case LVAL_ERR:
            free(v->value.err);
            break;
        case LVAL_SYM:
            free(v->value.sym);
            break;
        case LVAL_SEXPR:
            for (int i=0;i<v->value.sexpr1->count;i++){
                lval_del(v->value.sexpr1->cell[i]);
            }
            free(v->value.sexpr1->cell);
        default:break;
    }
}

lval* lval_add(lval* v,lval* x) {
    v->value.sexpr1->count ++;
    v->value.sexpr1->cell = realloc(v->value.sexpr1->cell,sizeof(lval*)*v->value.sexpr1->count);
    v->value.sexpr1->cell[v->value.sexpr1->count-1]=x;
    return v;
}

edit: 7.24 I killed the warning by defining them in this order. A complex struct is a nightmare for me, I gave up trying to deal with the pointer problem. Below is my new code, still with the bad pointer.

struct init_lval;
struct init_sexpr;
typedef struct init_sexpr sexpr;
union expr{
    long num;
    char* err;
    char* sym;
    sexpr* sexpr1;
};
typedef struct init_lval lval;

struct init_lval
{
    int type;
    union expr value;
};

struct init_sexpr{
   int count;
   lval** cell;
};
lval* lval_add(lval* v, lval* x) {
    v->value.sexpr1->count ++;
    v->value.sexpr1->cell = realloc(v->value.sexpr1->cell,sizeof(lval*)*v->value.sexpr1->count);
    v->value.sexpr1->cell[v->value.sexpr1->count-1]=x;
    return v;
}
void lval_del(lval* v){
    switch (v->type) {
        case LVAL_NUM:
            break;
        case LVAL_ERR:
            free(v->value.err);
            break;
        case LVAL_SYM:
            free(v->value.sym);
            break;
        case LVAL_SEXPR:
            for (int i=0;i<v->value.sexpr1->count;i++){
                lval_del(v->value.sexpr1->cell[i]);
            }
            free(v->value.sexpr1->cell);
            free(v->value.sexpr1);
        default:break;
    }
    free(v);
}

Answer 1

struct lval** cell; is invalid, you do not have a struct lval , you typedef ed an anonymous struct to lval .

Change it to lval **cell;

You also do not increment v->value.sexpr1->count in your add function, so it will always write to the same position.

Answer 2

the problem here is with realloc. You are trying to realloc the memory which is never malloced. In addition you need to allocate memory to sexpr1 before using it in the expressions like v->value.sexpr1->cell

Try this:

lval* lval_add(lval* v,lval* x) {
    v->value.sexpr1->count ++;
    if(v->value.sexpr1->cell == NULL) {
        v->value.sexpr1->cell = malloc(sizeof(lval*)*v->value.sexpr1->count);
    } else {
        v->value.sexpr1->cell = realloc(v->value.sexpr1->cell,sizeof(lval*)*v->value.sexpr1->count);
    }
    v->value.sexpr1->cell[v->value.sexpr1->count-1]= (struct lval*)x;
    return v;
}

And initialise the lval which is being passed to lval_add , like this:

lval *z = malloc(sizeof(lval));
z->value.sexpr1 = malloc(sizeof(sexpr));
z->value.sexpr1->cell= NULL;

Hope this helps!

Answer 3

Parameter type mismatch: Incompatible pointer types 'lval *' and 'struct anonymous::lval *'.

The above warning is because you have an anonymous struct. try:

typedef struct lval {
    int type;
    union expr value;
};

This should resolve this warning at least.