CODEWITHSUNDEEP
cpointersstructdeclaration
guhur
guhur

Reputation: 2866

Why my struct has an incomplete definition?

I am implementing a struct in C:

typedef struct {
...   
} _p_TSResilOnline;

typedef struct _p_TSResilOnline *TSResilOnline;

After (in the same file), I am using:

TSResilOnline         o  = (TSResilOnline)(chk->data);
...
*check = (o->threshold < PetscAbs(sf)) ? PETSC_FALSE : PETSC_TRUE;

But my compiler returns:

error: incomplete definition of type 'struct _p_TSResilOnline'
*check = (o->threshold < PetscAbs(sf)) ? PETSC_FALSE : PETSC_TRUE; ~^ note: forward declaration of 'struct _p_TSResilOnline' typedef struct _p_TSResilOnline *TSResilOnline;

I am wondering what is incomplete. The compiler should know everything.

Upvotes: 0

Views: 1118

Answers (1)

Vlad from Moscow
Vlad from Moscow

Reputation: 310950

In this declaration

struct {
...   
} _p_TSResilOnline;

you defined an object with identifier _p_TSResilOnline that has type of an unnamed structure.

In this declaration

typedef struct _p_TSResilOnline *TSResilOnline;

you declared structure type struct _p_TSResilOnline.

The identifier _p_TSResilOnline of the object and identifier _p_TSResilOnline used to name the structure in the typedef declaration are in different namespaces and identifies different entities.

The definition of struct _p_TSResilOnline is incomplete because members of the structure are unknown.

However in this expression

o->threshold

you are trying to access member with name threshold that was not declared.

So the compiler issues an error.

EDIT: After you changed the first declaration in your question the following way

typedef struct {
...   
} _p_TSResilOnline;

nevertheless again _p_TSResilOnline and struct _p_TSResilOnline are different entities and their identifiers belong to different name spaces.

You should write instead

struct _p_TSResilOnline {
...   
};

or

typedef struct _p_TSResilOnline {
...   
} _p_TSResilOnline;

Upvotes: 2

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