Pass string value to catch (Inner exceptions)

Question

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 { 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 { 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 + 
 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; }

Vulpes · 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 { 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 { 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
; message += String.Join(
 notDoubles.ToArray()); MessageBox.Show(message); Environment.Exit(0); } } return returnValue; }

Vulpes · Answer

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.

Vulpes · Answer

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.

Vulpes · Answer

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 Shariff · Answer

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 { 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 { 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 + 
 + .String Value Present in the Parametric Data - Exit Application  MessageBoxButtons.OK MessageBoxIcon.Error); Environment.Exit(0); } return returnValue; }

Vulpes · Answer

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
; message += String.Join(
 notDoubles.ToArray()); MessageBox.Show(message); return null; } // rest of code }

Vulpes · Answer

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
; message += String.Join(
 notDoubles.ToArray()); MessageBox.Show(message); return null; } // rest of code }

Vulpes · Answer

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
; message += String.Join(
 notDoubles.ToArray()); MessageBox.Show(message); return null; } // rest of code }

Farhan Shariff · Answer

Perfect :) You are one among the Best Teachers I have had thanks a lot Guru

Farhan Shariff · Answer

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 continued as col is declared outside this loop and also outside try statement

Farhan Shariff · Answer

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 Shariff · Answer

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.

Farhan Shariff · Answer

passing string doubleColName will overload the fuction as i am returing only one table

Farhan Shariff · Answer

No thats just an example yaar column names are way tooo complicated

Farhan Shariff · Answer

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)