Clever Geek Handbook

C: Incomplete return type

I tried to implement a linked list in C and started with this simple code:

#include <stdio.h>

struct int_node;
struct int_list;
struct int_list create_list();

int main() {

    struct int_list list = create_list();
    return 0;
}

struct int_node {
    int value;
    struct int_node * next;
};

struct int_list {
    struct int_node * first;
};

struct int_list create_list() {
    /* Creates an empty list, first node=null */
    struct int_list list;
    list.first = NULL;
    return list;
};

I got two errors when building:

  • Call 'create_list' with incomplete return type 'struct int_list'
  • The variable is of incomplete type 'struct int_list'

I was looking for an answer and all I could find was that I need to declare structures and functions before using them, which is what I did.

Another thing I tried was to move the main () function to the end and resolve the errors, but this is a stupid workaround and I want to find a real solution.

Any help?

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2 answers


Structure definitions must also be placed before main()

. That is, your stupid fix is ​​actually the correct fix.



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You actually need to define structs before using them, otherwise the compiler knows what it struct int_node

is when it sees it in the main method. Since Bill Lynch said your simple fix is ​​actually the right way.



You should look at exactly how the program goes from source code to executable in C if you are interested in learning more. Here's an interesting and short page about it.

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