CODEWITHSUNDEEP
cglib
Goaler444
Goaler444

Reputation: 2621

working at each iteration g_hash_table_foreach

I wish to loop through every key value pair within my hashtable. Therefore I used the g_hash_table_foreach() function (Prototype shown below). For each key value pair, it calls a void func method.

void g_hash_table_foreach(GHashTable *hash_table,GHFunc func,
                          gpointer user_data);

However, I require that for every call to the function, the method returns a value back.

For example consider the following code:

void calculate(gpointer key, gpointer value, gpointer userdata)
{
    return calculateNumbers(key, value);
}

int total = 0;
g_hash_table_foreach(mymap, calculate, NULL);

I require that the variable total stores the total of each returned value received by the calculate() function. I am finding it difficult to do this with the g_hash_table_foreach method.

I would rather have a while loop, declare the total variable outside and increase its value with every iteration over each pair. However, I dont think glib allows to me conider a key-value pair one at a time. (Unlike the GList with has the next attribute) Any ideas how I can do this please?

Upvotes: 4

Views: 4912

Answers (1)

unwind
unwind

Reputation: 399863

That's why the API gives you a "user pointer". Pass whatever data you need there, for instance the address of the total variable:

static void calculate(gpointer key, gpointer value, gpointer userdata)
{
    int *total = userdata;

    *total += calculateNumbers(key, value);
}

g_hash_table_foreach(mymap, calculate, &total);

The glib and GTK+ API:s are very good at providing user pointers, which has left me "spoiled"; whenever a see a C API involving callbacks that doesn't (forcing the programmer to use global state) I cringe. And complain. And, if possible, fix it.

UPDATE: Also, for completeness' sake, you actually can do this without the callback, using the GHashTable's "iteration" API.

See the g_hash_table_iter_init() and g_hash_table_iter_next() functions. These require at least glib version 2.16.

Upvotes: 7

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