值存储在结构中

Question

i'm new to C language. I have some questions to ask regarding structs.

For example:

static inline void *mmc_priv(struct mmc_host *host)
{        
     return (void *)host->private;
}

struct mmc_host 
{
    unsigned long private[0] ____cacheline_aligned;
};


struct mmc_davinci_host *host = NULL;
struct mmc_host *mmc = NULL;

host = mmc_priv(mmc);
host->mmc = mmc;

*for the struct mmc_davinci_host please refer to this site http://lxr.free-electrons.com/source/drivers/mmc/host/davinci_mmc.c#L167 *

The function mmc_priv() returns a void pointer. So, where does host store the returned address since host is a struct type?

Thank you.

Answer 1

Returning void* does not mean to return a void pointer. It means to return a pointer to any type .
In fact, pointers store addresses, and addresses always have the same size, no matter which type is located behind.

However, you should have a cast to struct mmc_davinci_host * after calling mmc_priv . I would write it as follows:

/* call mmc_priv and store its result in host, after having cast it to struct mmc_davinci_host * */
host = (struct mmc_davinci_host *) mmc_priv(mmc);