How to use a specific structure from another source file?

Question

I use Linux as my programming platform and C as a programming language.

My problem is that I define the structure in the main source file (main.c):

struct test_st { int state; int status; }; 

Therefore, I want this structure to be used in another source file (e.g. otherrc.). Is it possible to use this structure in another source file without putting this structure in the header?

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 definition of the structure. A good way is to define it in main.h and include it 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 find a better name than main.h

Answer 2

You can define the structure in each source file, then declare the instance variable once as global and once as 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; 

Then the linker will do the magic, and the source file will point to the same variable.

However, duplicating a definition in multiple source files is a bad coding practice, because in case of changes you need to manually change each definition.

A simple solution is to put the definition in the header file and then include it in the entire source file that uses the structure. To access a single instance of the structure in the source files, you can still use the extern method.

 // Definition.h struct test_st { int state; int status; }; // File1.c #include "Definition.h" struct test_st g_test; // File2.c #include "Definition.h" extern struct test_st g_test; 

Answer 3

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

By prohibiting this, you can treat main.c as a header file and include it in another file, and then compile another file. Or you can declare the same structure in both files and leave a note for yourself to change it in both places.

Answer 4

C support separate compilation .

Place the structure declaration in the header file and #include "..." in the source files.

Answer 5

 // use a header file. It 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); 

Answer 6

The header file / * includes this header file in file1.c and file2.c

 strcut a { }; struct b { }; 

therefore, the header file included the declaration of both structures.

 file 1.c 

strcut a xyz[10]; → struct a defined here

use struct b here in this file

 extern struct b abc[20]; /* now can use in this file */ 

file2.c

 strcut b abc[20]; /* defined here */ 

use strcut a defined in file1.c

 use extern struct a xyz[10]