Pointer as a structure variable in c

Question

When I use code like this :

typedef struct {
        int x;
        int *pInt;
} tData;

tData *ptData = malloc(sizeof(tData));

If i understand it right, i allocated memory with size of tData and returned adress to this allocated memory to pointer *ptData.

But what if i used this code :

typedef struct {
        int x;
        int *pInt;
} *tData;

If I want to allocate memory to this struct, do I need a struct name? Because for me, if I allocate like malloc(sizeof(*tData));, it seems to me like I am allocating memory only for the pointer, not for the structure itself. When I want to refer to data in this structure, do I need to use pointer to pointer to a struct?
It confuses me a bit and I couldn't find the answer I am looking for.
Thank you for any explanation!

Some discussion here. Apparently you should only typedef pointers like this "if your code will never dereference the pointer," — Karl Reid
– Karl Reid, Commented Oct 27, 2017 at 10:29
Closing as dupe, if this does not answer your question, let me know. — Sourav Ghosh
– Sourav Ghosh, Commented Oct 27, 2017 at 10:31
It didn't. They discussed there first form of code i posted. I have problem understanding the second one. And i can't avoid it, in this situation.. — SevO
– SevO, Commented Oct 27, 2017 at 10:41
You can use a struct name as you mentioned, or you can typedef both the struct type and the pointer to struct type like this typedef struct { ... } tData, *ptData; — Stuart
– Stuart, Commented Oct 28, 2017 at 0:24

Some programmer dude · Accepted Answer · 2017-10-27 10:30:15Z

3

This is one of the reason one should avoid creating type-aliases of pointers.

As for how to use it, instead of passing the type to the sizeof operator, use the variable. Like e.g.

typedef struct {
        int x;
        int *pInt;
} *tData;

tData ptData = malloc(sizeof *ptData);  // Allocate memory for one structure

answered Oct 27, 2017 at 10:30

Some programmer dude

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2 Comments

SevO Over a year ago

And may i ask, if i would change it to typedef struct data {...} *tData;, would struct data *pData; mean the same as tData pData; ?

Some programmer dude Over a year ago

@SevO Yes it would.

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