CODEWITHSUNDEEP
cstruct
Osley
Osley

Reputation: 103

What does `*` mean in a C `typedef struct` declaration?

I'm looking at a C struct with some syntax I've never seen before. The structure looks like this:

typedef struct structExample {
   int member1;
   int member2
} * structNAME;

I know that normally with a structure of:

typedef struct structExample {
   int member1;
   int member2
} structNAME;

I could refer to a member of the second struct definition by saying:

structNAME* tempStruct = malloc(sizeof(structNAME));
// (intitialize members)
tempstruct->member1;

What does that extra * in the the first struct definition do, and how would I reference members of the first struct definition?

Upvotes: 9

Views: 4505

Answers (5)

iain
iain

Reputation: 5683

The typedef makes these two statements the same

struct structExample *myStruct;
structName myStruct;

It makes structName stand for a pointer to struct structExample

As an opinion, I dislike this coding style, because it makes it harder to know whether a variable is a pointer or not. It helps if you have

typedef struct structExample * structExampleRef;

to give a hint that it is a pointer to struct structExample;

Upvotes: 2

harald
harald

Reputation: 6126

It means the defined type is a pointer type. This is an equivalent way to declare the type:

struct structExample {
    int member1;
    int member2;
};
typedef struct structExample * structNAME;

You would use it like this:

structNAME mystruct = malloc (sizeof (struct structExample));
mystruct->member1 = 42;

Upvotes: 6

unwind
unwind

Reputation: 399753

The secret to understanding these is that you can put typedef in front of any declaration, to turn TYPENAME VARIABLENAME into typedef TYPENAME ALIASEDNAME.

Since the asterisk can't be part of the VARIABLENAME part if this was a plain declaration, it has to be part of the type. An asterisk following a type name means "pointer to" the preceding type.

Compare this:

typedef int * my_int_pointer;

It's exactly the same, except in your case instead of int you're declaring a struct.

Upvotes: 1

Tapas Pal
Tapas Pal

Reputation: 7207

In that case (* structNAME) is pointer variable of that structure..

Upvotes: 0

UmNyobe
UmNyobe

Reputation: 22890

structNAME is defined as a pointer on struct structExample. SO you can do

structNAME tempStructPtr = malloc(sizeOf(struct structExample));
tempStructPtr->member1 = 2;

Upvotes: 1

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