Question

I am trying to find whether a certain path is a directory or not.

I’m using the stat function present in <sys/stat.h> using the following code:

int  isDir(char *path){
    printf("%s\n", path);
    struct stat file;
    stat(path, &file);
    printf("%i\n", file.st_mode);
    int x; 
    x = S_ISDIR(file.st_mode);
    return x;
}
// I tried this function with the following code.
    printf("%i\n",  isDir("/home/aladdin"));
    printf("%i\n",  isDir("/home/aladdn"));

My username on the PC is aladdin so, the first one should work and equal 1, and the second should print a 0, as there are no user named aladdn.

So running the previous code gives

/home/aladdin
16832
1
/home/aladdn
16832
1

Any idea about what’s wrong?

Answer 1

You must check stat return code. If stat fails, it will not modify your file struct contents, and in that case it IS_DIR seems to return true.

So, instead of your current line stat(path, &file);, have line:

if (stat(path, &file) == -1) return 0;

…of course you should probably report the error somehow, depending on your requirements, but that simple change will fix your function.

As to why you get identical results, I think C leaves structs like that uninitialized unless you explicitly initialize them, and with that kind of usage, the struct will be in exactly the same spot in stack on 2nd call, so it still has the values from 1st call. But this is just chance, change the code and behaviour changes unpredicably. C is fun that way 🙂

To zero the buf, do this before calling stat with &file:

memset(&file, 0, sizeof file);