Why segmentation fault in this HashTable code in Vala?

Question

I am trying following code of creating and showing a simple HashTable in Vala:

public static void myshowHashTable(HashTable sht){   
    stdout.printf("Size of sent hashtable: %d", (int)sht.size()); 
    sht.foreach((key,val) => {
            stdout.printf("Key:%s, value:%s", (string)key, (string)val);
        }
    ); 
}

public static void main(string[] args){
        HashTable<string,int> ht = new HashTable<string,int>(str_hash, str_equal); 
        ht.insert ("first string", 1);
        ht.insert ("second string", 2);
        ht.insert ("third string", 3);
        myshowHashTable(ht); 
}

Above code compiles with following warnings:

myhashtable.vala.c: In function ‘myshowHashTable’:
myhashtable.vala.c:45:29: warning: passing argument 2 of ‘g_hash_table_foreach’ from incompatible pointer type [-Wincompatible-pointer-types]
   45 |  g_hash_table_foreach (sht, ___lambda4__gh_func, NULL);
      |                             ^~~~~~~~~~~~~~~~~~~
      |                             |
      |                             void (*)(const void *, const void *, void *)
In file included from /usr/include/glib-2.0/glib.h:50,
                 from myhashtable.vala.c:4:
/usr/include/glib-2.0/glib/ghash.h:105:61: note: expected ‘GHFunc’ {aka ‘void (*)(void *, void *, void *)’} but argument is of type ‘void (*)(const void *, const void *, void *)’
  105 |                                             GHFunc          func,
      |                                             ~~~~~~~~~~~~~~~~^~~~

When I run the executable created, it give following error:

$ ./myhashtable
Segmentation fault

Where is the problem and how can it be solved?

Answer 1

I don't get about compilation warnings, but segmentation fault is pretty clear: you have HashTable<string,int>, but try to print (string)key, (string)val.

And you omit type specialization at sht argument. Therefore compiler couldn't deduce types.

I got it not crashing this way:

public static void myshowHashTable(HashTable<string,int> sht){   
    stdout.printf("Size of sent hashtable: %d\n", (int)sht.size()); 
    sht.foreach((key,val) => {
            stdout.printf("Key:%s, value:%d\n", key, val);
        }
    ); 
}