How to use a defined struct from another source file?

Question

Hi,

I am using Linux as my programming platform and C language as my programming language.

My problem is, I define a structure in my main source file( main.c):

struct test_st
{
   int state;
   int status;
};

So I want this structure to use in my other source file(e.g. othersrc.). Is it possible to use this structure in another source file without putting this structure in a header?

Thanks

Answer 1

You can use pointers to it in othersrc.c without including it:

othersrc.c:

struct foo
{
  struct test_st *p;
};

but otherwise you need to somehow include the structure definition. A good way is to define it in main.h, and include that in both .c files.

main.h:

struct test_st
{
   int state;
   int status;
};

main.c:

#include "main.h"

othersrc.c:

#include "main.h"

Of course, you can probably find a better name than main.h

Answer 2

Putting it in a header file is the normal, correct way to declare types shared between source files.

Barring that, you can treat main.c as a header file and include it in the other file, then only compile the other file. Or you can declare the same struct in both files and leave a note to yourself to change it in both places.

Answer 3

C support separate compilation.

Put structure declaration into a header file and #include "..." it in the source files.

Answer 4

You can define the struct in each source file, then declare the instance variable once as a global, and once as an extern:

// File1.c
struct test_st
{
   int state;
   int status;
};

struct test_st g_test;

// File2.c
struct test_st
{
   int state;
   int status;
};

extern struct test_st g_test;

The linker will then do the magic, both source file will point to the same variable.

However, this is the worst possible coding practice, and I can't see any good reason to do it.

Answer 5

// use a header file.  It's the right thing to do.  Why not learn correctly?

//in a "defines.h" file:
//----------------------

typedef struct
{
   int state; 
   int status; 
} TEST_ST; 


//in your main.cpp file:
//----------------------

#include "defines.h"

TEST_ST test_st;


    test_st.state = 1;
    test_st.status = 2;




//in your other.ccp file:

#include "defines.h"

extern TEST_ST test_st;

   printf ("Struct == %d, %d\n", test_st.state, test_st.status);