Using GLib's GArray to store `structs` and retrieve data

Question

I'm trying to use GLib as an alternative to write my own datastructures. My objective is to write a simple graph datastructure based on adjacency lists using only glib.

The code right now is the following

#include <glib.h>
#include <glib/gprintf.h>

struct graph
{
    GArray * nodes;
};

struct node
{
    GArray * neighbors;
    gint weight;
    GString * label;
};

struct neighbor
{
    struct node * dst;
    gint weight;
};

struct graph * graph_new(void);
void graph_node_add(struct graph * graph, const gchar * label, gint weight);
void graph_edge_add(struct graph * graph, struct node * src, struct node * dst, gint weight);

struct graph * graph_new(void)
{
    struct graph * g = g_new(struct graph, 1);
    g->nodes = g_array_new (FALSE, FALSE, sizeof (struct node));
    return g;
}

void graph_node_add(struct graph * graph, const gchar * label, gint weight)
{
    struct node * node = g_new(struct node, 1);
    node->neighbors = g_array_new(FALSE, FALSE, sizeof (struct neighbor));
    node->label = g_string_new(label);
    node->weight = weight;
    graph->nodes = g_array_append_val(graph->nodes, node);
}

void graph_edge_add(struct graph *graph, struct node *src, struct node *dst, gint weight)
{
    struct neighbor * neighbor = g_new(struct neighbor, 1);
    neighbor->dst = dst;
    neighbor->weight = weight;
    src->neighbors = g_array_append_val(src->neighbors, neighbor);
}


int main(void)
{
    struct graph * G = graph_new();
    graph_node_add(G, "u", 10);
    graph_node_add(G, "v", 20);
    graph_node_add(G, "w", 15);

    struct node * n = &g_array_index(G->nodes, struct node, 0);
    g_printf("segfaulting here\n");
    char * s = n->label->str;
    g_printf("LABEL %s\n", s);

    return(0);
}

It segfaults when retrieving the GString from struct node (around line 59).

Since I'm starting with GLib, any better approaches to handle my objectives are welcom.

Pay attention that I haven written the functions to free the memory, that is just to make the source code smaller in this question.

On linux the code can be compiled with:

gcc `pkg-config --cflags --libs glib-2.0` -o graph graph.c

Answer 1

This happens because in graph_node_add() you end up adding a single pointer to your array, not the data you wanted to add.

Something like this is likely to work:

struct node node;
node.neighbors = g_array_new(FALSE, FALSE, sizeof (struct neighbor));
node.label = g_string_new(label);
node.weight = weight;
graph->nodes = g_array_append_val(graph->nodes, node);