Redefinition errors in .h files

Question

//list.h file
typedef struct _lnode{
    struct _lnode *next;
    size_t row;
    size_t column;
    short data;
}lnode;

typedef struct _llist{
    struct _lnode *head;
    size_t size;

}llist;

//matrix.h file
typedef struct _matrix{

    size_t width;
    size_t height;
    size_t k;

    int **data;

}matrix;

//smatrix.h file
#include "list.h"
#include "matrix.h"

typedef struct _smatrix{
    size_t width;
    size_t height;
    size_t k;

    llist data;
}smatrix;

smatrix* make_smatrix(matrix *m);

smatrix.h file includes list.h file and matrix.h files. If I include those header files in smatrix.h file then I get

 redefinition of 'lnode'. redefinition of '_llist' and redefinition of '_matrix' errors.

If I took those heder files our from smatrix.h file then the error went away but it complains about matrix type in the function parameter. I want to call functions defined in list.h and matrix.h files in smatrix.c file.. What do I do? Thanks in advance..

Answer 1

Possible problem of multiple inclusions.

Try to guard your header files with #ifndef read about it here

file list.h

#ifndef _LISTH_
#define _LISTH_

<your code>

#endif

file matrix.h

#ifndef _MATRIXH_
#define _MATRIXH_

<your code>

#endif

It will prevent you too have redefinitions if you have a loop in header inclusions.

Answer 2

你需要在头文件中包含警卫 。

Answer 3

Well from your posted code what I think is missing is at the beginning of each *.h file:

#ifndef _some_unique_identifier_for_each_header 
#define _some_unique_identifier_for_each_header

...header contents

#endif //_some_unique_identifier_for_each_header

or a

#pragma once 

if your compiler supports it.

Without this, if the header is included multiple times from various sources you get errors relating to redefinition.

Answer 4

You probably include smatrix.h and list.h in some other file. You should avoid that. The usual way to do that is to use include guards .

These are macros that you check with #ifdef at the beginning of the file (with #endif in the end), and #define them inside the #ifdef ... #endif , thus insuring that even if you do include the same file multiple times, the compiler will only read it once, at the first time, and skip all the rest.