Re: Adding the ability to add functions into structures?

Albert a écrit : 
So structures are useful to group variables, so you can to refer to a
collection as a single entity. Wouldn't it be useful to also have the
ability to collect variable and functions?

Ask K&R say, C programs consist of variables to store the input and
functions to manipulate them.

This would make C object-oriented - how cool would that be?

Are there any problems with adding the ability to have functions
encapsulated in structures?

You can do this by defining an interface. I do this by using the following schema:

The object has a pointer to the interface, called "lpVtbl", and other
fields.

The interface is a set of function pointers that defines the methods
available for the object.

For instance:

1) I define a forward declaration to the object
typedef struct _ArrayList ArrayList;

2) I define the interface functions:
typedef struct {
        // Returns the number of elements stored
        int (*GetCount)(ArrayList &AL);
        // Is this collection read only?
        int (*IsReadOnly)(ArrayList &AL);
        // Sets this collection read-only or unsets the read-only flag
        int (*SetReadOnly)(ArrayList &AL,int flag);
	///SNIP /// SNIP /// SNIP
        // Pushes a string, using the collection as a stack
        int (*Push)(ArrayList &AL,void *str);
} ArrayListInterface;

3) I define the object
struct _ArrayList {
        ArrayListInterface *lpVtbl; // The table of functions
        size_t count;             /* number of elements in the array */
        void **contents;          /* The contents of the collection */
        size_t capacity;    /* allocated space in the contents vector */
        unsigned int flags;             // Read-only or other flags
        size_t ElementSize; // Size of the elements stored in this array
};

The usage is now very simple: For instance to get the count of elements
in an array list I do:

	ArrayList al;
	/// snip initialization, etc

	int count = al.lpVtbl->GetCount(&al);

The lcc-win32 compiler uses this feature extensiveley to define arraylists and other data structures in C.

jacob
.

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