Generic list manipulation function in C?

Question

What is a generic list manipulation function in C? (I saw this when I was going through some materials.)

What is the difference between this function and a function

Answer 1

As mentioned above, I tried using MACROS approach to create the list manipulation functions. Its easy to create the INSERT operation routine but difficult to create Delete and traverse operations. Following it the list structure and the INSERT routine signature:

#define LIST_DEFINE(type) \
    struct list_node_##type \
    { \
        type *data; \`
        struct list_node_##type *next; \
   };

LIST_INSERT(&ListHead,&Data, DataType);

Where:
ListHead - Head of the linked list
Data - The Data for which a new node will be created and data is inserted in the node DataType - Is the data-type of the data passed

FYI, I am allocating memory in the function and copying all the data passed in the newly created node and them append the node in linked list.

Now, when a LIST_DELETE routine is created, the node needs to be deleted will be identified using a unique identifier within the data. That identifier is also passed in the MACRO routine as key that will be replaced in the MACRO expansion. The routine signature could be:

LIST_DELETE(&ListHead, DataType, myvar->data->str, char*);

Where:
ListHead - Head of the linked list
DataType - Is the data-type of the data
myvar->data->str - Unique key
char* - Key type

Now, when the key is expanded, that same key cannot be used for comparison as if we write

if((keytype)ListHead->data->key == (keytype)key)

It expands to

ListHead->data->myvar->data->str == myvar->data->str

And here there is no variable like: ListHead->data->myvar->data->str

So, this approach cannot work to write delete routines and as the traversal and search routines also use unique key, same problem will be faced in them as well.

And, on an unrelated note, how to determine the matching logic for unique key, as the unique key could be anything.