CODEWITHSUNDEEP
cstruct
KaramJaber
KaramJaber

Reputation: 893

C - What is this code line means?(about structs)

If i want to define a struct in c i write

typedef struct ObjectP
{
   some code
}

and this is legal, but what about this code line ? 

typedef struct Object* ObjectP
{
   some code
}

why there is a syntax error on the line typedef struct Object* ObjectP

Upvotes: 0

Views: 133

Answers (4)

0xF1
0xF1

Reputation: 6116

You are using wrong syntax for typedefing the struct pointer.

Use:

typedef struct Object
{
   some code
}
*ObjectP;

Now you can use ObjectP to define pointers to this struct this way: ObjectP ptr1_struct, ptr2_struct;.

Upvotes: 2

Pala
Pala

Reputation: 2171

Structure definition should end with ";". typedef is not part of structure definition. It is a renaming convention.

Upvotes: 1

John Bode
John Bode

Reputation: 123458

The syntax for a struct definition is

    struct identifieropt { struct-declaration-list }

The optional identifier is the struct tag; it's the name by which the struct type can be referenced. For example:

struct foo { int x; int y; double z; };

foo is the tag for that struct type; I can then use struct foo anywhere I need a type name:

struct foo bar;
struct foo *fptr;

I can combine the struct definition and object declaration in one:

struct foo { int x; int y; double z; } bar, *fptr;

If I want to create a typedef name for a pointer to struct foo, I do it as follows:

typedef struct foo { int x; int y; double z} *FooP;

FooP is now a synonym for struct foo *:

FooP myptr;

is equivalent to

struct foo { int x; int y; double z; } *myptr;

Upvotes: 0

Some programmer dude
Some programmer dude

Reputation: 409136

That's not how you use typedef with structures. You have to put the type-alias name after the structure, like

typedef struct Object
{
    ...
} Object;

And if you want multiple type-aliases, you just add them to then end, as in

typedef struct Object
{
    ...
} Object, *ObjectP;

Or you separate the definitions:

struct Object
{
    ...
};

typedef struct Object Object;
typedef struct Object *ObjectP;

Upvotes: 5

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