问题
I try to save the SQL Results in a array and return it back. but i'm getting an exception: array out of range error.
here is my code:
public BookingUpdate[] getBookingUpdates(string token)
{
String command = "SELECT b.ID,b.VERANSTALTER, rr.VON ,rr.BIS, b.THEMA, b.STORNO, ra.BEZEICHNUNG from BUCHUNG b JOIN RESERVIERUNGRAUM rr on rr.BUCHUNG_ID = b.ID JOIN RAUM ra on ra.ID = rr.RAUM_ID WHERE b.UPDATE_DATE BETWEEN DATEADD (DAY , -20 , getdate()) AND getdate() AND b.BOOKVERNR = 0";
SqlConnection connection = new SqlConnection(GetConnectionString());
BookingUpdate[] bookingupdate = new BookingUpdate[1];
connection.Open();
try
{
SqlCommand cmd = new SqlCommand(command, connection);
SqlDataReader rdr = null;
int count = 0;
rdr = cmd.ExecuteReader();
while (rdr.Read())
{
DataTable dt = new DataTable();
dt.Load(rdr);
count = dt.Rows.Count;
for (int c = 0; c < count; c++)
{
bookingupdate = new BookingUpdate[c];
bookingupdate[c].bookingID = (long)rdr["ID"]; // <---- Error is here
bookingupdate[c].fullUserName = rdr["VERANSTALTER"].ToString();
bookingupdate[c].newStart = (DateTime)rdr["VON"];
bookingupdate[c].newStart = (DateTime)rdr["BIS"];
bookingupdate[c].newSubject = rdr["THEMA"].ToString();
bookingupdate[c].newlocation = rdr["BEZEICHNUNG"].ToString();
if (rdr["STORNO"].ToString() != null)
{
bookingupdate[c].deleted = true;
}
else
{
bookingupdate[c].deleted = false;
}
}
}
}
catch (Exception ex)
{
log.Error(ex.Message + "\n\rStackTrace:\n\r" + ex.StackTrace);
}
finally
{
connection.Close();
}
return bookingupdate;
}
What am i missing?
回答1:
You appear to be creating and allocating memory for an array with
bookingupdate = new BookingUpdate[c];
but not actually creating instances of BookingUpdate. When you attempt to set properties on your array element there is no actual BookingUpdate to update - there is only a holder for one.
I'd suggest changing your code to something along the lines of:
...
bookingupdate = new BookingUpdate[count]; // allocates space for the number of BookingUpdates to be created
for (int c = 0; c < count; c++)
{
bookingupdate[c] = new BookingUpdate(); // create a new instance of BookingUpdate and assign it the array
bookingupdate[c].bookingID = (long)rdr["ID"];
...
I hope that this helps!
回答2:
bookingupdate = new BookingUpdate[c];
bookingupdate[c].bookingID = (long)rdr["ID"];
you are creating an Array of length c, which means it has the Indexes 0 to (c-1) - and then you are out of bounds, when trying to store at Position c.
回答3:
Imho i would simplify your way to construct that array with Linq:
BookingUpdate[] bookingupdate = dt.AsEnumerable()
.Select(r => new BookingUpdate{
bookingID = r.Field<long>("ID"),
fullUserName = r.Field<string>("VERANSTALTER"),
newStart = r.Field<DateTime>("Von"),
newEnd = r.Field<DateTime>("Bis"), // here was another bug in your originalcode
newSubject = r.Field<string>("THEMA"),
newlocation = r.Field<string>("BEZEICHNUNG"),
deleted = r.Field<string>("STORNO") != null
})
.ToArray();
On this way you will not have problems with arrays that are out of bounds.
回答4:
You accessing the n'th element of an n-Elements array which is out of range, you need to access the n - 1 element.
bookingupdate = new BookingUpdate[c]; // You create an array of 5 elements for example
bookingupdate[c].bookingID = (long)rdr["ID"]; // Here you access the 5th elements but there are only 4
回答5:
the problem is related with the size of the array;
for (int c = 0; c < count; c++)
{
bookingupdate = new BookingUpdate[c];
bookingupdate[c].bookingID = (long)rdr["ID"];
in the previous code, you are creating an array (bookingupdate ) of size 0 at first; then you are trying to insert an item. Even if you somehow manage to skip first one, it will again fail. Just update these lines to the following;
bookingupdate = new BookingUpdate[count];
for (int c = 0; c < count; c++)
{
bookingupdate[c].bookingID = (long)rdr["ID"];
回答6:
for (int c = 0; c < count; c++)
{
bookingupdate = new BookingUpdate[c];
Error is at first iteration of this for loop where c is zero. ie, you are trying to create a array of length zero. bookingupdate = new BookingUpdate[0];
回答7:
You have initialized an array but not the class itself before calling it. Also your initialization is wrong
count = dt.Rows.Count;
bookingupdate = new BookingUpdate[count];
for (int c = 0; c < count; c++)
{
bu = new BookingUpdate();
bu.bookingID = (long)rdr["ID"]; // <---- Error is here
bu.fullUserName = rdr["VERANSTALTER"].ToString();
bu.newStart = (DateTime)rdr["VON"];
bu.newStart = (DateTime)rdr["BIS"];
bu.newSubject = rdr["THEMA"].ToString();
bu.newlocation = rdr["BEZEICHNUNG"].ToString();
if (rdr["STORNO"].ToString() != null)
{
bu.deleted = true;
}
else
{
bu.deleted = false;
}
bookingupdate[c] = bu;
}
回答8:
Arrays has zero based index.
When you create bookingupdate = new BookingUpdate[c]; your last index would c-1.
You can't access BookingUpdate[c] because it is not exist.
Let's say c = 4, that means we definedan array with 4 elements which they are;
BookingUpdate[0]
BookingUpdate[1]
BookingUpdate[2]
BookingUpdate[3]
BookingUpdate[c] would equal BookingUpdate[4] which there is no such an index.
From MSDN page;
Arrays are zero indexed: an array with n elements is indexed from 0 to n-1.
回答9:
Use this code
public BookingUpdate[] getBookingUpdates(string token)
{
String command = "SELECT b.ID,b.VERANSTALTER, rr.VON ,rr.BIS, b.THEMA, b.STORNO, ra.BEZEICHNUNG from BUCHUNG b JOIN RESERVIERUNGRAUM rr on rr.BUCHUNG_ID = b.ID JOIN RAUM ra on ra.ID = rr.RAUM_ID WHERE b.UPDATE_DATE BETWEEN DATEADD (DAY , -20 , getdate()) AND getdate() AND b.BOOKVERNR = 0";
BookingUpdate[] bookingupdate;
SqlConnection connection = new SqlConnection(GetConnectionString());
connection.Open();
try
{
SqlCommand cmd = new SqlCommand(command, connection);
SqlDataReader rdr = null;
int count = 0;
rdr = cmd.ExecuteReader();
while (rdr.Read())
{
DataTable dt = new DataTable();
dt.Load(rdr);
count = dt.Rows.Count;
bookingupdate = new BookingUpdate[count];
for (int c = 0; c < count; c++)
{
bookingupdate[c].bookingID = (long)rdr["ID"]; // <---- Error is here
bookingupdate[c].fullUserName = rdr["VERANSTALTER"].ToString();
bookingupdate[c].newStart = (DateTime)rdr["VON"];
bookingupdate[c].newStart = (DateTime)rdr["BIS"];
bookingupdate[c].newSubject = rdr["THEMA"].ToString();
bookingupdate[c].newlocation = rdr["BEZEICHNUNG"].ToString();
if (rdr["STORNO"].ToString() != null)
{
bookingupdate[c].deleted = true;
}
else
{
bookingupdate[c].deleted = false;
}
}
}
}
catch (Exception ex)
{
log.Error(ex.Message + "\n\rStackTrace:\n\r" + ex.StackTrace);
}
finally
{
connection.Close();
}
return bookingupdate;
}
来源：https://stackoverflow.com/questions/14849780/indexing-array-out-of-range-exception