C compilation error : called object is not a function-CodePudding

I have created a macro for initializing a structure with some data, including a callback function pointer because this code is extensively reused in my file. I am storing the function pointer so I can simply iterate over the structure without having to explicitly check the msg_id and call the corresponding handling function.

These lines of code are around line number 150 :

typedef struct my_struct {
    some_list        *child_list;
    void             *data;
    void             *msg_func;
    int              nesting_level;
    int              msg_id;
} my_struct_t;
                                                                                                                                                                                                                                                                                                                                                                                                                                                         
#define MALLOC_STRUCT_WITH_BASIC_DATA(level, msg_id, data_arg)     \
    my_struct_t *new_child = NULL;                                 \
    MY_CALLOC(new_child, my_struct_t, 1, failure);                 \                                          
    LISTCREATE(new_child->child_list);                             \
    new_child->data = data_arg;                                    \                                                            
  
#define INIT_MY_STRUCT(level, msg_id, data_arg, child_func)        \
if (some_condition_on_data_arg_is_satisfied(data_arg)) {           \
    MALLOC_STRUCT_WITH_BASIC_DATA(level, msg_id);                  \
    new_child->msg_func = &child_func;                             \                                        
    (new_child->msg_func)(new_child, new_child->data);             \
}

There are about 100 msg functions and the list will keep increasing in the future. Their declarations are around line 250 :

static void msg_function1(my_struct_t *st, data_type1 *ptr_data);
static void msg_function2(my_struct_t *st, data_type2 *ptr_data);
...
static void msg_functionn(my_struct_t *st, data_typen *ptr_data);

Finally, the macros are invoked around line number 580 and message handling functions are defined starting around line number 700.

I get a compilation error when the macro is encountered : my_file.c:586: error: called object ‘new_child->msg_func’ is not a function

This is my first time using function pointers. I searched on stackoverflow and google and tried to eliminate possible causes, including ordering of function declaration and usage. Could someone please help me understand what am I doing wrong here? To note, I do not have permission to change the message handling functions' type to void * or something else.

CodePudding user response：

You need to have a function pointer not an "ordinary" void pointer in your structure.

typedef struct my_struct {
    some_list        *child_list;
    void             *data;
    void             (*msg_func)(my_struct_t *, void *);
    int              nesting_level;
    int              msg_id;
} my_struct_t;

Ten message functions should convert the void pointer to the correct object pointer

static void msg_function2(my_struct_t *st, void *vData)
{
    data_type2 *ptr_data = vData;
    /* ... */