Re: std::list::iterator

From:

Victor Bazarov <v.bazarov@comcast.invalid>

Newsgroups:

comp.lang.c++

Date:

Mon, 25 Aug 2014 16:26:44 -0400

Message-ID:

<ltg665$msf$1@dont-email.me>

On 8/25/2014 2:54 PM, Christopher Pisz wrote:

I am curious why the following code compiles if a list iterator is
forward only

Isn't it bidirectional? I mean, if this compiles, it must be, no?

> and I am doing a -- on it. It doesn't seem to work though,

because my string ended with a comma on it when I expected it not to end
with a comma.

---------------

int main()
{
     std::list<std::string> orderIDs;

     // SNIP fill it

     std::string orderIDsAsString; // String of order IDs seperated by
commas

     for(std::list<std::string>::iterator itOrderID = orderIDs.begin();
itOrderID != orderIDs.end(); ++itOrderID)
     {
         orderIDsAsString += *itOrderID;

         if(itOrderID != --orderIDs.end())
         {
             orderIDsAsString += ",";
         }
     }
    return 0;
}

----------
So, I changed the code to this

----------
int main()
{
     std::list<std::string> orderIDs;

     // SNIP fill it

     std::string orderIDsAsString; // String of order IDs seperated by
commas

     std::string orderIDsAsString;
     for(std::list<std::string>::iterator itOrderID = orderIDs.begin();
itOrderID != orderIDs.end(); ++itOrderID)
     {
         orderIDsAsString += *itOrderID;
         orderIDsAsString += ",";
     }

     orderIDsAsString.erase(orderIDsAsString.end() - 1); // Get rid of
last comma

    return 0;
}

--------

Following Jorgen's advice, change your code to

     for (std::list<std::string>::iterator ... ) // like yours
     {
        if (itOrderID != orderIDs.begin())
           orderIDsAsString += ",";
        orderIDsAsString += *itOrderID;
     }

and your problem shall be solved, no need to erase, no doubt about the
operator--.

V
--
I do not respond to top-posted replies, please don't ask