#include "glib.h"
#include <stdio.h>



typedef struct MyType
{
    int a;
}mytype_t;



int main(int argc, char* argv[])
{
    printf("startn");

    mytype_t myt;

    GList *l = NULL;

    for(int i=0;i<10;i++)
    {
        myt.a = i;
        l = g_list_append(l, &myt);
    }


    printf("length: %dn", g_list_length(l));

    printf("5th item a value: %dn", ((mytype_t)g_list_nth_data(l,4))->a );



    return 0;
}

The compiler (gcc) don`t compile it.
output:
gcc -o "main" "main.c" -g -Wall -std=c99 `pkg-config --cflags --libs glib-2.0` (/home/pi/projektek/glist/glist könyvtárban)
main.c: In function ‘main’:
main.c:26:2: error: conversion to non-scalar type requested
  printf("5th item a value: %dn", (int)((mytype_t)g_list_nth_data(l,4))->a );
  ^~~~~~
Fordítás sikertelen.