Thread: compile error: storage size of 'var' isn't known

Hello everyone,


I get a strange compile error when compile such simple program. Any ideas?

foo.c: In function `main':
foo.c:5: error: storage size of 'var' isn't known

foo.c

Code:

#include "goo.h"

int main (int argc, char** argv)
{
    t_st var;
    var.member = 100;
    return 0;
}

goo.c

Code:

struct st {

int member;

};

goo.h

Code:

typedef struct st t_st;

thanks in advance,
George

So how did you compile your program. did you linked your library with your main program while compiling.

ssharish2005

You define the structure in a .c file. How can any other module possibly know about it?

Both the structure and the typedef should be in goo.h, and there should be no file goo.c.

Definitely, yes! Any ideas?

Originally Posted by ssharish2005

So how did you compile your program. did you linked your library with your main program while compiling.

ssharish2005

regards,
George

Thanks, do you mean any structure definition (real implementation) must be in .h in C? I have seen many program written by others which define (implement) struct in .c other than .h.

Originally Posted by brewbuck

You define the structure in a .c file. How can any other module possibly know about it?

Both the structure and the typedef should be in goo.h, and there should be no file goo.c.

regards,
George

Thanks Salem, do you mean in order to access the member of a struct, we have to define struct in .h and includes it, or else we could only access its member variable inside the same .c file? No walk-arounds?

Originally Posted by Salem

Well goo.c has the actual structure, so there is no way for foo.c to know what the members are.

All that goo.h does is basically confirm that a struct called st exists.

In foo.c, you could have
t_st *var;
but you still would not be able to access any members within that struct.

It is, in other words an incomplete type.

Incomplete types are very useful for implementing opaque interfaces. goo.h declares an opaque pointer, which any user just sees the pointer.
The actual content of the struct is private to goo.c.

It's what FILE* should be - all user code just passes around a FILE* without ever knowing what is behind it.

regards,
George