Passing an array of structs to a function

I have the following code. I have a method called SendBookDiffs(MTBookDiff *bookdiffs, UINT bookdiffs_total) which I would like to use. The description for this method is "This method accepts array of MTBookDiff structures, counting 'bookdiffs_total' elements."

So what I have tried is the following:

MTBookDiff *bookdiffs;
MTBookItem items[128];
bookdiffs->items = it开发者_高级运维ems;

But I encountered a "error C2106: '=' : left operand must be l-value" error. According to some replies, I have tried

memcpy(bookdiffs->items, items, sizeof(bookdiffs->items));

But is there the proper way of executing it? Thanks! Edited: Simplifying the question asked.

Based on the

#define MAX_PATH          260

enum EnMTAPIConstants
  {
   MT_SYMBOL_LEN              =32,                          
   MT_BOOK_DEPTH              =32,                          
   MT_ADDRESS_LEN             =64,                          
   MT_NEWSUBJECT_LEN          =256,                         
   MT_NEWSCATEGORY_LEN        =256,                         
   MT_LOGIN_LEN               =64,                          
   MT_PASSWORD_LEN            =64,                          
   MT_PARAMS_LEN              =256,                         
   MT_DESCRIPTION_LEN         =MAX_PATH                     
  }

struct MTBookItem
  {
   enum EnBookItemType
     {
      ItemReset=0,                                          
      ItemSell =1,                                          
      ItemBuy  =2                                          
     };
   UINT              type;                                  
   double            price;                                 
   INT64             volume;                                
   UINT              reserved[8];                           
  };

struct MTBookDiff
  {
   wchar_t           symbol[MT_SYMBOL_LEN];                 
   MTBookItem        items[MT_BOOK_DEPTH*4];                
   UINT              items_total;                           
   UINT              reserved[64];                          
  };

MTBookDiff *bookdiffs;
MTBookItem items[128];
bookdiffs->items = items;

you can't assign an array to another array as you do.

instead since you are anyway using C++, use vector

vector<MTBookItem> items

You need to distinguish between a[] and *a. The first allocated a block of memory big enough to hold the specified number of elements, leaving the variable pointing at the first. The second is just a pointer, which doesn't necessarily point at anything yet and which can be repointed elsewhere.

At risk of using an unpopular notation, Hungarian notation strictly distinguishes between ax and px, where the former is an array and the latter is a pointer. What's confusing is that you can pass ax to a function taking px, in which case the parameter is a pointer that is initialized to the first element of ax. However, while you can assign a pointer a new value, you can't do that for an array.

You need to do one of the following:

• memcpy(bookdiffs->items, items, sizeof(bookdiffs->items)
• change the type of the items fields from MTBookItem items[] to MTBookItem *items.

EDIT Given that this is a C++ question, using a std::vector as others have suggested is almost certainly better than either of my two suggestions.