storage size of DIR variable is not known

Question

The code of the faulty function is:

#include <stdio.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#define _ISDIR 1729
#define _ISFILE 431
#define _EXIST_ERR 611
#define _BUF_LEN 512
unsigned int fod(char*);
unsigned int fod(char *name){
    DIR check_dir;
    check_dir=opendir(name);
    int openf=open(name,O_RDONLY);
    if(check_dir!=NULL){
        return _ISDIR;
    }
    if(openf!=-1){
        return _ISFILE;
    }
    return _EXIST_ERR;
}

When I compile it with gcc 12.1.1, I get the following error:

copy.c:14:9: error: storage size of ‘check_dir’ isn’t known
   14 |     DIR check_dir;
      |         ^~~~~~~~~

How do I fix it? the function parameters are right, everyone says that this is how a directory should be opened. How do I fix it?

Answer 1

It doesn't compile because DIR struct is not fixed and you need to use a pointer to DIR instead. Also, opendir returns *DIR too. So replace this:

DIR check_dir;

With this:

DIR *check_dir;

You can check the return type by reading opendir manual page. The function is declared like this:

DIR *opendir(const char *name);

(Notice the return type)