Why doesn't it increment?

Question

So I was trying to do a function that take a GTree* a (each node of the Tree is a struct User) and an idand it would search for that user and increment a variable! (school project)

With some help from here, I managed to do but I didn't realize that it was not incrementing.

The structure is:

typedef struct user {
    int id;
    char username[256]; 
    int post_count; 
    char short_bio[16384]; 
    int reputation;
}*USER;

typedef struct TCD_community{
    GTree* res;    
    GTree* quest; 
    GTree* users; /
}TCD_community;

typedef struct TCD_community * TAD_community;

TAD_community tq;

And function is (helped by a stackoverflow user):

void incrementaPost(GTree* a,int id){

    gpointer ptr = g_tree_lookup ( a , &id);   

    struct user *u = (struct user *) ptr; 

    if(u){
        u->post_count++;  
    }
}

I called that on main like:

incrementaPost( tq -> users, 703994);

Output:

Id 703994 
Name N.Sinha 
post_count 0 
reputation 51

Expected:

Id 703994 
Name N.Sinha 
post_count 1 
reputation 51

Answer 1

Please be aware that the GTree* has to be properly constructed before you can do the search.

First construct the tree with the dedicated search function:

GTree   *tree;
tree = g_tree_new(MySearchFunction);

Where

g_tree_new ()

GTree * g_tree_new (GCompareFunc key_compare_func);

Creates a new GTree.

Parameters:

key_compare_func

the function used to order the nodes in the GTree. It should return values similar to the standard strcmp() function -0 if the two arguments are equal, a negative value if the first argument comes before the second, or a positive value if the first argument comes after the second.

Then your objects have to inserted using g_tree_insert ()

g_tree_insert ()

void g_tree_insert (GTree *tree, gpointer key, gpointer value);

Inserts a key/value pair into a GTree.

If the given key already exists in the GTree its corresponding value is set to the new value. If you supplied a value_destroy_func when creating the GTree, the old value is freed using that function. If you supplied a key_destroy_func when creating the GTree, the passed key is freed using that function.

Parameters

tree

• a GTree

key

• the key to insert

value

• the value corresponding to the key

Only then, you can use g_tree_lookup for the search.

Check this simple example - how to construct GTree*, insert elements, do the search via g_tree_lookup and traverse the tree via g_tree_traverse.