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void pointer to struct pointer cast

Victor Yokota

I declared a void pointer

void *ptr;

and a typedef struct named testStructure, with a member 'unsigned int a'.

Now I will cast this pointer to a struct pointer:

ptr=(testStructure*)malloc(sizeof(testStructure));

Now I try to access the member of the struct...

ptr->a=5;

...and I get an error "expression must have a pointer-to-struct-or-union type"...
Why is 'ptr' still void? It seems, a void pointer cannot be casted to any other pointer type...
How I can do this properly?
I just need ONE pointer, which can point to different structures, that means, I need to cast a void pointer...

Parents
  • 0 in reply to Victor Yokota

    It's the same kind of mistake as the first time. As Andy said, if you want dynStructArray to be a pointer to an array of tDSA's, then why not declare it as such? It will save you many unnecessary type casts:

    struct DSA;

typedef struct DSA tDSA;

struct DSA
{
int p1,p2;
tDSA **dynStructArray;
};

tDSA *parent;


    Now you allocate memory:

    parent=malloc(sizeof(tDSA));
parent->dynStructArray=malloc(sizeof(*(parent->dynStructArray)));
(parent->dynStructArray)[0]=malloc(sizeof(tDSA));


    Then you can access the only element of the array like this:

    (parent->dynStructArray)[0]->p1=5;

Reply
  • 0 in reply to Victor Yokota

    It's the same kind of mistake as the first time. As Andy said, if you want dynStructArray to be a pointer to an array of tDSA's, then why not declare it as such? It will save you many unnecessary type casts:

    struct DSA;

typedef struct DSA tDSA;

struct DSA
{
int p1,p2;
tDSA **dynStructArray;
};

tDSA *parent;


    Now you allocate memory:

    parent=malloc(sizeof(tDSA));
parent->dynStructArray=malloc(sizeof(*(parent->dynStructArray)));
(parent->dynStructArray)[0]=malloc(sizeof(tDSA));


    Then you can access the only element of the array like this:

    (parent->dynStructArray)[0]->p1=5;

Children
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