Thread: Dereferencing a Void Pointer in a Structure

Hey all,

Hopefully this is a simple question for someone with more void* experience than me.

Say I have a data structure:

Code:

typedef struct sp_cntl_tag 
{
	void* pad;
	uint8 type;
	uint8 index;
} sp_cntl_t

and a function which takes a pointer to this structure as an input. Because of the 'type' variable, I know what the void pointer contains and would like to dereference it.

How do I dereference a void* from a structure? My instinct was to do something like

Code:

sp_cntl_t* temp;
desiredType = *temp->(typecast)pad;

but this didn't work... suggestions?

I do this for threads frequently and here is a little snippet.

Code:

struct s_data
{
    SOCKET sck;
    char *host;
    char *ip;
    unsigned short port;
};

DWORD WINAPI s_listen (void *params)
{
    struct s_data *data = (struct s_data *)params;

    printf("The host is %s\n", data->host);

Originally Posted by simpsonseric

My instinct was to do something like

Code:

sp_cntl_t* temp;
desiredType = *temp->(typecast)pad;

but this didn't work... suggestions?

Looks like you just put the cast in the wrong spot.

Code:

...

sp_cntl_t* temp = make_sp_cntl_t();

...

if (temp->type == SUPER_TYPE)
{
   super_type st = *(super_type*)temp->pad;
}

...

// or, breaking it down into individual actions:

if (temp->type == SUPER_TYPE)
{
   void *ptr = temp->pad;
   super_type *super_ptr = (super_type*)ptr;
   super_type st = *super_ptr;
}

...

thanks for the help