Array type has incomplete element type?

Question

I am trying to write a program that passes information from the kernel space to the user space on ububtu 14.04. I declared a struct as the follows:

typedef struct
{
   long pid;
   char TTY[64];
   unsigned long long time; 
   char COMM[64]
  } myTasks;

In main, I then create an array of myTasks structs like:

struct myTasks taskInfo[2500]; 
//do stuff 
syscall(__NR_my_syscall2,numTasks,sizeof(taskInfo),taskInfo); // use it here

However, when I do that, I get a error on this line saying:

struct myTasks taskInfo[2500] Error: array type has incomplete element

What am I doing wrong? I wanted to create an array of myTasks structs that I could pass as a buffer to a syscall... but I can't figure out what I'm doing wrong. I'm new to C so any help would be greatly appreciated.

Are you sure about that syscall? Aren't you missing a closing parentheses somewhere? — Some programmer dude, Feb 18 '16 at 09:35
@JoachimPileborg Thanks! However, thankfully its a mistake I only made typing it here :) — ocean800, Feb 18 '16 at 09:36
Does this answer your question? [C Compile Error: array type has incomplete element type](https://stackoverflow.com/questions/21080744/c-compile-error-array-type-has-incomplete-element-type) — Krishna Kanth Yenumula, Dec 02 '20 at 16:51

score 4 · Accepted Answer · answered Feb 18 '16 at 09:34

4

You typedefed the anonymous struct to myTasks. To declare your array, use myTasks taskInfo[2500].

C thinks you are declaring a new named struct struct myTasks, and it's incomplete because you didn't define the struct. However, myTasks is an alias for the struct you already defined.

answered Feb 18 '16 at 09:34

Purag

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Oh.. so the it's a problem in my understanding of structs? So I should look into something like [this](http://stackoverflow.com/questions/1675351/typedef-struct-vs-struct-definitions)? – ocean800 Feb 18 '16 at 09:39
1

Yeah, that's a great resource! It looks like you just have some confusion on naming of the structs. In the code you provided, the struct you defined doesn't have a name; it's *anonymous*. You declared `myTasks` as an alias for that struct type. So it's like assigning a nickname to the struct. Later, you tried to declare an array containing `struct myTask`s, and `struct myTask` doesn't actually exist. C thought you were going to declare a new struct there, and since you didn't, it gave the error. – Purag Feb 18 '16 at 09:41
Thanks!! That makes a lot more sense, and I'll definitely read more into that link. – ocean800 Feb 18 '16 at 09:44

score 2 · Answer 2 · answered Feb 18 '16 at 09:35

2

myTasks is a type-alias and not a structure name. The correct use of it is e.g.

myTasks taskInfo[2500];

answered Feb 18 '16 at 09:35

Some programmer dude

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Thanks for the answer!! :) – ocean800 Feb 18 '16 at 09:44

Array type has incomplete element type?

2 Answers2