Pointers to structs being passed to function

Question

This is a stripped down version of my program. I need to pass a pointer to pointers of structs to a function, modify the structs within the function, and have those changes persist. The function declaration must stay the same.

Currently I can modify the data within the function, but once returned to main, no changes were made.

Thank you for your help.

int main()
{
    struct node** HuffmanNodes;
    read_Huffman_encoded_data(&HuffmanNodes);
}

void read_Huffman_encoded_data(**HuffmanNodes)
{
    Huffman_node = (node**)malloc(sizeof(node*)*(*number_of_nodes));

    int index;
    for(index=0; index<*number_of_nodes;index++)
    {
        Huffman_node[index] = (node*)malloc(sizeof(node));
        Huffman_node[index]->first_value=1;
        Huffman_node[index]->second_value=2;
    }
}

Answer 1

You have a pointer typing problem. I'm surprised that it even compiles since &HuffmanNodes is of type node*** .

Try this:

void read_Huffman_encoded_data(struct node ***HuffmanNodes)
{
    *Huffman_nodes = (node**)malloc(sizeof(node*)*(*number_of_nodes));

    int index;
    for(index=0; index<*number_of_nodes;index++)
    {
        (*Huffman_nodes)[index] = (node*)malloc(sizeof(node));
        (*Huffman_nodes)[index]->first_value=1;
        (*Huffman_nodes)[index]->second_value=2;
    }
}

You also have some naming mismatches (which I fixed), I hope those are just typos from stripping down the program.

EDIT: Alternative Method

int main()
{
    struct node** HuffmanNodes = (node*)malloc(sizeof(node) * (*number_of_nodes));
    read_Huffman_encoded_data(HHuffmanNodes);
}

void read_Huffman_encoded_data(struct node **HuffmanNodes)
{
    int index;
    for(index=0; index<*number_of_nodes;index++)
    {
        Huffman_nodes[index] = (node*)malloc(sizeof(node));
        Huffman_nodes[index]->first_value=1;
        Huffman_nodes[index]->second_value=2;
    }
}

Answer 2

Try this:

int main()
{
    struct node** HuffmanNodes;
    read_Huffman_encoded_data(&HuffmanNodes);
}

void read_Huffman_encoded_data(**HuffmanNodes)
{
    Huffman_node = (node*)malloc(sizeof(node)*(number_of_nodes));

    int index;
    for(index=0; index<*number_of_nodes;index++)
    {
        Huffman_node[index] = (node*)malloc(sizeof(node));
        Huffman_node[index]->first_value=1;
        Huffman_node[index]->second_value=2;
    }
}