Just a questions regarding structures

[inu11byte]

I just have a question regarding structures. I have commented the source accordingly. Cheers.

#include<dirent.h>
#include<stdio.h>
 
int main(void)
 {
    DIR            *d;
    struct dirent  *dir; //How are these structures defined when there isn't a stucture set?
    d = opendir("."); // and why is dir a pointer?
 
 
    if (d)
    {
          while ((dir = readdir(d)) != NULL)
          {
             printf("%s\n", dir->d_name);
          }
      }
      
closedir(d);
getchar();


return 0;
}

[memcpy]

Wat? Copied from here? Unix shell scripts (C)

> How are these structures defined when there isn't a stucture set?
What's a structure set?

> and why is dir a pointer?
Because opendir() returns a pointer.

[anduril462]

They're defined in dirent.h, which is a header file defined on *nix systems. Read the man pages for opendir, readdir and closedir for more info. It's a pointer because that's how they designed it, probably​ so they could allocate memory and return that. You would have to ask whoever wrote it for more info.

[inu11byte]

Wat? Copied from here? Unix shell scripts (C)

> How are these structures defined when there isn't a stucture set?
What's a structure set?

> and why is dir a pointer?
Because opendir() returns a pointer.

What do you mean it returns a pointer? Could you give a brief explanation?

And the code has

 structdirent  *dir;

but there is no structure created. E.g. I expected to see

struct dirent{
    char name[20];
    int age;
    float salary;
}

Something along those lines...

[whiteflags]

Maybe you'd see it if you looked (well enough into) dirent.h, but you aren't supposed to care what that contains. It's a library for working with directories, and much of the programming interface (the part that you interact with) merely expects you to provide a pointer to an initialized dirent structure. The opendir function initializes said structure and returns a pointer to it. The closedir function frees the pointer.

Also I'm really amused that you think a dirent structure is like a salaryman.

[inu11byte]

So why could a structure be used when a structure wasn't defined with elements?

EDIT: Just looked in the dirent.h file and saw that it has the structure defined in there. Thanks for all the help. *facepalm*

[anduril462]

So why could a structure be used when a structure wasn't defined with elements?

It was defined with elements, in dirent.h. When you #include <dirent.h>, the compiler pastes the contents of dirent.h directly into your C file at that point, so it knows about the elements of the struct.