Partial Updating of Struct in a Vector

[jwwicks]

Hello Experts,

This is a student question and I know you could use a list or some other keyed container but they haven't been introduced to the class so they aren't free game so to speak.

So...Given a struct And a vector of those structs is their a way to partially update just first_name and last_name. I can find an account using a simple bool function and find_if but trying to use that iterator causes an error.

struct customer{
	string account;
	string first_name;
	string last_name;
	string address;
	string city;
	string state;
	string zip;
	string phone;
	double acct_balance;
	Date* date;
};

vector<customer> customers;
string t, id;
typedef vector<customer>::const_iterator VCI;

// Call a function to get account id from user
// This works fine

// Find the customer in the vector with the account id
// This works fine
t = id;
transform( t.begin(), t.end(), t.begin(), toupper );
VCI f = find_if( customers.begin(), customers.end(), cust_eq(t));

// Create a little temporary to get new information
customer* uCust = new( customer );
customer& cUpdate = *uCust;

// Call some function to just get the first_name and last_name into cUpdate
// This works fine...
do_cust_name( cUpdate );

//but use the following code
(*f).first_name = cUpdate.first_name;

// produces main.cpp(249): error C2678:
//binary '=' : no operator found which takes a left-hand
//operand of type 'const std::string' (or there is no acceptable conversion)

Why is this const now?? Should I, Can I, cast const away in this context??

I can't use a wholesale copy because only part of the members of the struct are actually updated...

Can't use customer.at() since I don't have an index...

Some hints please...

DUH! answered my own question just looked at the code above I used a const_iterator should have used iterator instead. That fixed it.

Is there a better way to do this ??

JWEMAIL REMOVED BY MODERATOR.

[RRick]

You've got the right idea. Iterators will allow you to modify the internal values to the struct in the vector. Const iterators won't allow you to change the values.

There is a simple nit-pick where you don't need to new and set a reference before passing it to do_cust_name. Your temporary can be a local variable and you'll get the same results.
[code=cpp]customer cUpdate;
do_cust_name( cUpdate );[/code]

[weaknessforcats]

(*f).first_name = cUpdate.first_n ame;

// produces main.cpp(249): error C2678:
//binary '=' : no operator found which takes a left-hand
//operand of type 'const std::string' (or there is no acceptable conversion)

You did not include <string>.

[jwwicks]

You've got the right idea. Iterators will allow you to modify the internal values to the struct in the vector. Const iterators won't allow you to change the values.

There is a simple nit-pick where you don't need to new and set a reference before passing it to do_cust_name. Your temporary can be a local variable and you'll get the same results.
[code=cpp]customer cUpdate;
do_cust_name( cUpdate );[/code]

Thanks for the feedback...

John

[jwwicks]

You did not include <string>.

Umm, not quite. I just didn't post the whole main etc.. trying to be brief to spare forum members. The #include <string> is there, it was just that the typedef vector<customer >::const_iterat or should have been just typedef vector<customer >::iterator.

Thanks for the feedback though...

John

[weaknessforcats]

Oops. I missed the part about const std::string in the error message.

I'm going for more coffee now.

Sorry.

[jwwicks]

Just a follow on to ask about style...

I have the following function and it works fine updating the information in the vector of structs. The question I have is should I change the cUpdate reference from *uCust to *f and just update the element in the vector directly without the use of a temp. The do_cust_xxxx functions all take a customer& as an argument. I'm toying with the idea since I don't see anything in C++ that say I can't do customer cUpdate& = *f; That would eliminate all the (*f).this_value = cUpdate.this_va lue; stuff right?

/////////////////////////
// \fn do_update( vector<customer>& c )
// \brief Handling routine for update menu
//
// \b Purpose: Processes update menu choices
// \b SideEffects: none
//
// \param c - vector containing customer records
// \return none
/////////////////////////
void do_update( vector<customer>& c )
{
	bool done = false;
	int choice;
	string t, id;

	customer* uCust = new( customer );
	customer& cUpdate = *uCust;
	
	do{
		system(CLRSCR);
		show_copyright();
		do
		{
			id = get_customer_id();
			cout << endl << "Modifying Customer : " << id << endl << endl;
		}while(!is_valid_customer_id( c, id ));

		typedef vector<customer>::iterator VCI;
		t = id;
		transform( t.begin(), t.end(), t.begin(), toupper );
		VCI f = find_if( c.begin(), c.end(), cust_eq(t));
		
		show_update_menu();
		do{ 
			choice = get_choice(); 
		}while(!is_valid_update_choice( choice )); 
		
		switch( choice ){
			case 1: do_cust_name( cUpdate );
					(*f).first_name = cUpdate.first_name;
					(*f).last_name = cUpdate.last_name;
					done = true;
					break;
			case 2: do_cust_address( cUpdate );
					do_cust_city( cUpdate );
					do_cust_state( cUpdate );
					do_cust_zip( cUpdate );
					(*f).address = cUpdate.address;
					(*f).city = cUpdate.city;
					(*f).state = cUpdate.state;
					(*f).zip = cUpdate.zip;
					done = true;
					break;
			case 3: do_cust_phone( cUpdate );
					(*f).phone = cUpdate.phone;
					done = true;
					break;
			case 4: do_cust_balance( cUpdate );
					(*f).acct_balance = cUpdate.acct_balance;
					done = true;
					break;
			case 5: do_cust_payment( cUpdate );
					(*f).date = cUpdate.date;
					done = true;
					break;
			default:
				done = true;
				break;
		}

	}while(!done);

	delete uCust;
}

John