Pass string value to catch (Inner exceptions)

Farhan Shariff

I have this function which compares two DataTables (table1 and table2 )and makes a a new table3( sorted in ascending order)

1.Here table2 should have only numeric(double) values but whenever there is a non numeric value I want to display the column name(col).

private static DataTable CompareTwoDataTable(DataTable table1, DataTable table2)
{

DataTable returnValue = null;

try
{
DataTable table3 = new DataTable();
DataRow dr = null;
string filterExp = string.Empty;
for (int i = 0; i < table1.Rows.Count; i++)
{

string col = table1.Rows[i]["Par Name"].ToString(); // column names of table2
if (table2.Columns.Contains(col) )
{
if (!table3.Columns.Contains(col))
{
table3.Columns.Add(col, typeof(double));
filterExp = filterExp + col + " asc ,";
}

for (int j = 0; j < table2.Rows.Count; j++)
{
if (table3.Rows.Count != table2.Rows.Count)
{
dr = table3.NewRow();
table3.Rows.Add(dr);
}
/*Here I want to check if the value begin copied is numeric(double) else I want to display the col (ie column name in table2)whenever there is a non numeric value control is transferred to catch how to pass col to catch */

table3.Rows[j][col] = table2.Rows[j][col];

}

}

}

returnValue = resultDt;
}

catch
{

MessageBox.Show("Critical Data error caused by "+ "\n" 1.String Value Present in the Parametric Data", "- Exit Application ", MessageBoxButtons.OK, MessageBoxIcon.Error);

MessageBox.show("Column with non numeric data :" +_______ );

Environment.Exit(0);

}

return returnValue;
}

15 Replies

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Vulpes12y ago
Accepted answer
What I had in mind is something like this (off 'top of head', untested):

private static DataTable CompareTwoDataTable(DataTable table1, DataTable table2)
{
DataTable returnValue = null;
var notDoubles = new List();
string col = null;

try
{
DataTable table3 = new DataTable();
DataRow dr = null;
string filterExp = string.Empty;
for (int i = 0; i < table1.Rows.Count; i++)
{
col = table1.Rows[i]["Par Name"].ToString(); // now using outer variable
if (table2.Columns.Contains(col))
{
try
{
if (!table3.Columns.Contains(col))
{
table3.Columns.Add(col, typeof(double));
filterExp = filterExp + col + " asc ,";
}

for (int j = 0; j < table2.Rows.Count; j++)
{
if (table3.Rows.Count != table2.Rows.Count)
{
dr = table3.NewRow();
table3.Rows.Add(dr);
}

table3.Rows[j][col] = table2.Rows[j][col];
}
}
catch // assume no other exceptions possible except type mismatch
{
notDoubles.Add(col);
}
}
}

if (notDoubles.Count == 0) returnValue = table3;
}
catch (Exception ex)
{
MessageBox.Show(ex.Message, MessageBoxButtons.OK, MessageBoxIcon.Error);
Environment.Exit(0);
}
finally
{
if (notDoubles.Count > 0)
{
string message = "The following columns are not doubles\r\n";
message += String.Join("\r\n", notDoubles.ToArray());
MessageBox.Show(message);
Environment.Exit(0);
}
}

return returnValue;
}
Farhan Shariff12y ago
Perfect :) You are one among the Best Teachers I have had thanks a lot Guru
Vulpes12y ago
That's right.

The nested try statement is wholly within the for loop. So when a mis-match exception occurs and is caught and handled by the catch block, control simply returns to the next iteration of the for loop.

The list and the 'col' variable are available throughout the for statement because we've declared them outside the outer try statement which includes the for statement and hence the inner catch block.
Farhan Shariff12y ago
So when data Mis-match happens when copying
table3.Rows[j][col] = table2.Rows[j][col];
control is transfered to
catch
{
notDoubles.Add(col);
} copying col to List

then control shifts back to
for (int i = 0; i < table1.Rows.Count; i++) and loop is continued as col is declared outside this loop and also outside try statement
Vulpes12y ago
One thing that can catch anyone out (me included) in try/catch/finally statements is variable scope.

If you declare a variable in the try block then it's scoped to that block and so isn't available in the catch and finally blocks. This surprises a lot of people but it's the way it works in C#.

To ensure that they're available everywhere what I did here was to declare both the list and 'col' completely outside the nested try statements.

I also put the code which checks whether there were any mismatches and prints them out in the finally block of the outer try block.

This means that, even if there's some exception other than a type mismatch, the user will still see the mismatches which have been identified to date before the application exits. That's because you're guaranteed that the finally block will always run whether there's an exception or not.
Farhan Shariff12y ago
Works Perfectly fine I had forgotten about finally-thanks a lot Vuples

When col is declared as null and used how is the control transfered back
Farhan Shariff12y ago
I totally agree and understand what you are saying, but is possible to jump to and fro from catch block to outer loop each time exception is generated and also use a list in catch block to record the column name.how to transfer control back.
In my scenario is it very strict that no numeric or null values are to be present as the input files are machine generated and this non numeric value may very rarely arise only due to user interference, I have included the code only to check user error.
Vulpes12y ago
The only weakness I can see with using nested exceptions is that, as you currently have it, the application will exit on finding the first non-double column.

If you wanted to report all of them, you could add them to a list rather than calling Environment.Exit in the inner catch block. After all the code has run, you could then see if there are any names in the list and, if there are, print them out and exit the application at that point.

The code to do this could be put in a finally block for the outer try.
Farhan Shariff12y ago
I found another way by using nested try and catch

try
{

DataTable table3 = new DataTable();
DataRow dr = null;
string filterExp = string.Empty;
for (int i = 0; i < table1.Rows.Count; i++)
{

string col = table1.Rows[i]["Par Name"].ToString();
if (table2.Columns.Contains(col))
{
try
{
if (!table3.Columns.Contains(col))
{
table3.Columns.Add(col, typeof(double));
filterExp = filterExp + col + " asc ,";
}

for (int j = 0; j < table2.Rows.Count; j++)
{
if (table3.Rows.Count != table2.Rows.Count)
{
dr = table3.NewRow();
table3.Rows.Add(dr);
}

table3.Rows[j][col] = table2.Rows[j][col];

}

}
catch
{
MessageBox.Show("Parameter Has non numeric Values: " +col);
Environment.Exit(0);
}

}

}

returnValue = resultDt;

}

catch
{

MessageBox.Show("Critical Data error caused by either "+ "\n" + .String Value Present in the Parametric Data", "- Exit Application ", MessageBoxButtons.OK, MessageBoxIcon.Error);

Environment.Exit(0);

}

return returnValue;
}
Farhan Shariff12y ago
passing string doubleColName will overload the fuction as i am returing only one table
Vulpes12y ago
Here's some more general code:

private static DataTable CompareTwoDataTable(DataTable table1, DataTable table2, string doubleColName)
{
var doubles = new List();

foreach(DataRow dr in table1.Rows)
{
doubles.Add(dr[doubleColName].ToString());
}

var notDoubles = new List();

foreach(DataColumn dc in table2.Columns)
{
if(!doubles.Contains(dc.ColumnName)) continue; // ignore non-matching columns
if (dc.ColumnType != typeof(double)) notDoubles.Add(dc.ColumnName);
}

if (notDoubles.Count > 0)
{
string message = "The following columns are not doubles\r\n";
message += String.Join("\r\n", notDoubles.ToArray());
MessageBox.Show(message);
return null;
}

// rest of code
}
Farhan Shariff12y ago
No thats just an example yaar column names are way tooo complicated
Vulpes12y ago
In that case perhaps you could modify the code as follows:

private static DataTable CompareTwoDataTable(DataTable table1, DataTable table2)
{
var notDoubles = new List();

foreach(DataColumn dc in table2.Columns)
{
if(!dc.ColumnName.StartsWith("Par")) continue; // ignore non-Par columns
if (dc.ColumnType != typeof(double)) notDoubles.Add(dc.ColumnName);
}

if (notDoubles.Count > 0)
{
string message = "The following columns are not doubles\r\n";
message += String.Join("\r\n", notDoubles.ToArray());
MessageBox.Show(message);
return null;
}

// rest of code
}
Farhan Shariff12y ago
table2 has columns with string values also
here only those columns names which are under "Par Name" column of table1 have to be considered while copying to table3.
basically all column names(in Par Name) are of double

table1

ParName

Par1

Par2

Par3

Par4

table2

starttime
Par1
Tag
Par2
Par4
Par3

##
1.2
Normal
1.23
121
1.22

##
1.4
Normal
MARS
121
2.4

##
1.5
normal
6.2
212
3.2

here Par2 has MARS i want to handle these kind of situations and indicate to user under which column it is happening (which rarely happen)
Vulpes12y ago
Why don't you just iterate through the columns in table2 to make sure they're all doubles before attempting to do any copying?

private static DataTable CompareTwoDataTable(DataTable table1, DataTable table2)
{
var notDoubles = new List();

foreach(DataColumn dc in table2.Columns)
{
if (dc.ColumnType != typeof(double)) notDoubles.Add(dc.ColumnName);
}

if (notDoubles.Count > 0)
{
string message = "The following columns are not doubles\r\n";
message += String.Join("\r\n", notDoubles.ToArray());
MessageBox.Show(message);
return null;
}

// rest of code
}

starttime	Par1	Tag	Par2	Par4	Par3
##	1.2	Normal	1.23	121	1.22
##	1.4	Normal	MARS	121	2.4
##	1.5	normal	6.2	212	3.2