How do I prevent the code below from throwing a FormatException. I'd like to be able to parse strings with a leading zero into ints. Is there a clean way to do this?
string value = "01";
int i = int.Parse(value);
Your code runs for me, without a FormatException (once you capitalize the method properly):
string value = "01";
int i = int.Parse(value);
But this does ring an old bell; a problem I had years ago, which Microsoft accepted as a bug against localization components of Windows (not .NET). To test whether you're seeing this, run this code and let us know whether you get a FormatException:
string value = "0"; // just a zero
int i = int.Parse(value);
EDIT: here's my post from Usenet, from back in 2007. See if the symptoms match yours.
For reference, here's what we found.
The affected machine had bad data for
the registry value
[HKEY_CURRENT_USER\Control Panel
\International\sPositiveSign].
Normally, this value is an empty
REG_SZ (null-terminated string). In
this case, the string was missing its
terminator. This confused the API
function GetLocaleInfoW(), causing it
to think that '0' (ASCII number zero)
was the positive sign for the current
locale (it should normally be '+').
This caused all kinds of havoc.
You can verify this for yourself with
regedit.exe: open that reg value by
right-clicking on the value and
selecting 'Modify Binary Data'. You
should see two dots on the right
(representing the null terminator).
If you see no dots, you're affected.
Fix it by adding a terminator (four
zeros).
You can also check the value of
CultureInfo.CurrentCulture.NumberFormat.PositiveSign;
it should be '+'.
It's a bug in the Windows localization
API, not the class libs. The reg
value needs to be checked for a
terminator. They're looking at it.
...and here's a report on Microsoft Connect about the issue:
Try
int i = Int32.Parse(value, NumberStyles.Any);
int i = int.parse(value.TrimStart('0'));
TryParse will allow you to confirm the result of the parse without throwing an exception. To quote MSDN
Converts the string representation of
a number to its 32-bit signed integer
equivalent. A return value indicates
whether the operation succeeded.
To use their example
private static void TryToParse(string value)
{
int number;
bool result = Int32.TryParse(value, out number);
if (result)
{
Console.WriteLine("Converted '{0}' to {1}.", value, number);
}
else
{
if (value == null) value = "";
Console.WriteLine("Attempted conversion of '{0}' failed.", value);
}
}
You don't have to do anything at all. Adding leading zeroes does not cause a FormatException.
To be 100% sure I tried your code, and after correcting parse to Parse it runs just fine and doesn't throw any exception.
Obviously you are not showing actual code that you are using, so it's impossible to say where the problem is, but it's definitely not a problem for the Parse method to handle leading zeroes.
Try
int i = Convert.ToInt32(value);
Edit: Hmm. As pointed out, it's just wrapping Int32.Parse. Not sure why you're getting the FormatException, regardless.
I have the following codes that may be helpful:
int i = int.Parse(value.Trim().Length > 1 ?
value.TrimStart(new char[] {'0'}) : value.Trim());
This will trim off all extra leading 0s and avoid the case of only one 0.
For a decimal number:
Convert.ToInt32("01", 10);
// 1
For a 16 bit numbers, where leading zeros are common:
Convert.ToInt32("00000000ff", 16);
// 255
Related
I have a Oracle-view which gives me those data:
DATUM STUNDE LAUFZEIT
-------------- ---------- -----------
30.10.14 00:00 11 ,433333333
The column LAUFZEIT is declared as NUMBER. Which format to I need to convert the column to get 0,433333333 or rounded to 0,4?
I already tried some types like Convert.ToSingle(reader.GetValue(2)) but always get a error like
System.OverflowException: Arithmetic operation resulted in an overflow
Thanks!
You have to mention a currect Culture:
Object source = ",433333333";
// This will fail with exception - Neutral Culture uses decimal point, not comma
//Single single = Convert.ToSingle(source, CultureInfo.InvariantCulture);
// OK: Russian culture (ru-RU) uses decimal comma, not decimal point
Single single = Convert.ToSingle(source, new CultureInfo("ru-RU"));
To represent the value in desired form, use formatting, e.g. for 0,4:
// F1 - one floating point
// "ru-RU" for decimal comma
String result = single.ToString("F1", new CultureInfo("ru-RU"));
Edit: having seen on the Exception stack trace, i.e.
Arithmetic operation resulted in an overflow. at Oracle.DataAccess.Types.DecimalConv.GetDecimal(IntPtr numCtx)
one can conclude that the problem is in the
`Oracle.DataAccess.Types.DecimalConv.GetDecimal`
the origin of the error may be in the fact that Oracle Number(36) or the the like is bigger that .Net Decimal. Since you can't change Oracle.DataAccess library you can convert to String just in the query:
select ...
cast(LAUFZEIT as VarChar2(40)),
...
you can always add a leading zero yourself before parsing. Adding a zero to the start of a number will NEVER change it.
Convert.ToSingle('0' + reader.GetString(2).Replace(',','.')) should do it.
I advice to use reader.GetString() before parsing.
Also it would be better to do:
Single a ;
if(Single.TryParse('0' + reader.GetString(2).Replace(',','.')), out a))
{
//Success code here
}
else
{
//Code to execute if string was not parsable here
}
In this way you won't get an exception
So I am still learning C#, and i have a bit of a problem. I am making a very simple windows forms application, with two text boxes, input and Output, For conversions from hex to dec. Here is my code:
string input = textBox1.Text;
int Output = Convert.ToInt32(input, 16);
textBox2.Text = Output.ToString();
//Textbox1 is Input
//Textbox2 is Output
There are potentially two exceptions you're going to run into here. First, is a FormatException like you described. This can occur if the input string isn't formatted correctly; say it contains a non hex character, a space, or something else. The other exception you will encounter is an overflow exception, when the hex from the first text box becomes a number too large for a 32 bit integer.
To handle the exceptions, you're going to need a try catch block. Check out https://msdn.microsoft.com/en-us/library/0yd65esw.aspx for more info on the try catch.
A better way of writing this with some error checking might look like something below:
string input = textBox1.Text;
try
{
int Output = Convert.ToInt32(input, 16);
textBox2.Text = Output.ToString();
}
catch (FormatException)
{
MessageBox.Show("Input string is not in the correct format.");
}
catch (OverflowException)
{
MessageBox.Show("Input is too large for conversion.");
}
//Textbox1 is Input
//Textbox2 is Output
As Shar1er80 and Landepbs have pointed out, the code you provided won't error if your input is correct. It's your job as the programmer to validate that the input will not error. You can do an error check with a regular expression as Shar1er80 has suggested, but there are other ways as well. You will not only need to check that the input contains valid characters for conversion to hex, you also should check the length. Each Hex character can be one of 16 possible values (0-F). Putting two of them together yields 256 possible values, or exactly one byte. A 32 bit integer is 4 bytes, meaning your maximum length of valid input is 8 characters. Any more, and the integer will overflow.
You should also decide if you want to use a signed integer as you have or an unsigned integer. In signed integers, one bit is used for the sign, so the largest positive integer you can output is half what it would be for an unsigned integer. You can read more about integers and sign at https://msdn.microsoft.com/en-us/library/5kzh1b5w.aspx.
Good luck learning C# and stick with it!
What is the problem? This code looks good with one exception, HEX is limited to 0 - 9 and A - F. I would suggest adding input validation for this.
EDITED:
Check this SO answer for validating hex input
Check a string to see if all characters are hexadecimal values
How do I check the empty check boxes which convert strings to integers using "int.Parse" in C#?
If I try to pass blank text boxes, visual studio gives me this error - "Input string was not in a correct format."
I already read some questions on stackoverflow which address the same issue, but I know that various people use various methods to do the same task. So I would like to know them as well. Please start with the simplest way you know first.
int multiplyBy;
if(int.TryParse(textBox3.Text, out multiplyBy)) {
//success
} else {
//string was not in correct format
}
The int.TryParse(string s, out int result) method trys to parse the string, but throws no exception if the format is wrong, it returns a bool indicating if the format was valid. The out int result parameter is the int wich should get the value.
Use Int32.TryParse to verify that the value in the text box is a valid integer
http://msdn.microsoft.com/en-us/library/f02979c7.aspx
You can check if the textbox has a value with:
string.IsNullOrEmpty(textbox.Text)
if you want it in single line of code
vb.net
int i = If(String.IsNullOrEmpty(TextBox1.Text), 0, Int32.Parse(TextBox1.Text))
c#
int i = (String.IsNullOrEmpty(TextBox1.Text)) ?? 0: Int32.Parse(TextBox1.Text)
Instead of directly parsing string representation into integer, check whether it is able to convert in integer. .NET has TryParse method of integer which tries to convert the string representation into int , and returns the bool value indicates whether the conversion succeeded. And if succeeded, stores the parsed value in second parameter of TryParse function which is of out type.
Note: TryParse method does not throw an exception if the conversion fails. It simply returns false indicates that conversion is got failed.
Ref : http://msdn.microsoft.com/en-us/library/f02979c7.aspx
Why don't you just catch the exception
try
{
int multiplyBy = int.Parse(textBox3.Text);
} catch(Exception){}
You can also catch(FormateException) if you like.
Hope this helps!
I am trying to format a decimal (as a percentage without the % sign), displaying brackets () around negative numbers and displaying positive numbers as is.
var returnString = value.HasValue
? string.Format("{0:0.0;(0.0)}", value.Value * 100) :
DefaultEmptyString;
return returnString;
My main problem is that for a numbers such as -0.000491 which in this formatting scheme is a zero it should still show the brackets as it is a negative zero.
Nonetheless, it is being lost.
I could stop using the section separator and utilize an if statement instead but it seems like the section separator should do the trick.
Any ideas why the formatting is not done correctly ?
Any ideas why the formatting is not done correctly ?
Is is done correctly according to the documentation:
If the number to be formatted is negative, but becomes zero after rounding according to the format in the second section, the resulting zero is formatted according to the first section.
Since I don't see any options available that would override that default behavior, one option is to append the parentheses manually:
public string Format(decimal value)
{
string s = (value*100).ToString("0.0;0.0");
if(value < 0)
s = "(" + s + ")";
return s;
}
From the documentation: http://msdn.microsoft.com/en-US/library/0c899ak8%28v=vs.80%29.aspx
"If the number to be formatted is negative, but becomes zero after rounding according to the format in the second section, then the resulting zero is formatted according to the first section."
The formatting is correct, you will need the if statement.
I am attempting to validate a date text box to make sure the correct date format was entered.
I converted this vb6 code:
If (IsDate(txtBirthDate)) And (IsNumeric(Right(txtBirthDate, 4))))
into this C# code -
int output = 1;
DateTime output2;
if ((! DateTime.TryParse(txtBirthDate.Text, out output2)) & (!int.TryParse((txtBirthDate.Text.Substring(txtBirthDate.Text.Length - 5)), out output)))
{
MessageBox.Show("error")
}
What I am attempting to do is make sure that the last 4 digits of the date text box are numeric (the year - i.e 1990 in 05/10/1990) and if it is not a number, then show error. Although I cannot verify everything is numeric due to the "/" in the date format.
The code does not show an error and builds. But when I debug the application I receive an error. The error states:
Index and length must refer to a location within the string.
Parameter name: length.
Any ideas on how to accomplish this?
To check if a date is in a specific format, use DateTime.TryParseExact():
if (!DateTime.TryParseExact(output , "d/M/yyyy", CultureInfo.InvariantCulture, DateTimeStyles.None, out output2))
{
MessageBox.Show("error")
}
EDIT: Change the format according to your needs:
"d/M/yyyy" for UK and "M/d/yyyy" for US
Edit: It sounds like the cause of your error is your string is too short. Test the string length before you test the last 4 characters.
Three other issues:
The And operator in C# is &&. You are using & which is a bitwise operator.
To check the last four characters of the string, you should use .Length - 4, not 5.
You are negating the return values in your C#, but not in your VB. To match the VB, omit the !. But, it looks like that's not what you are actually trying to do. It looks like you want to show an error message if either the string is not parsable as a date or the year portion is not 4 digits. In that case use a an or comparison (||):
if (!DateTime.TryParse(txtBirthDate.Text, out output2) ||
txtBirthDate.Text.Length < 4 ||
!int.TryParse((txtBirthDate.Text.Substring(txtBirthDate.Text.Length - 4)), out output))
{
MessageBox.Show("error")
}
Keep in mind that yyyy/M/d is also parsable as a Date, contains a 4-digit year, but will fail your test. Is that what you want?
From the error provided it looks like you just need a length check to make sure you can process the code. You should also use && instead of & (or in this case probably ||) to ensure that the boolean expressions stop executing once a true state has been encountered.
if (txtBirthDate.Text.Length < 5 ||
(!DateTime.TryParse(txtBirthDate.Text, out output2) ||
!int.TryParse((txtBirthDate.Text.Substring(txtBirthDate.Text.Length - 5)), out output)))
{
MessageBox.Show("error")
}
However, this might be a good case for the use of a regular expression.
Regex reg = new Regex("^\d{2}/\d{2}/\d{4}$");
if (!reg.IsMatch(txtBirthDate.Text))
MessageBox.Show("error");
Tweaking of the regular expression to match fringe cases (leading zero's, alternate formats, etc) may be necessary.
int result;
if (int.TryParse(txtBirthDate.Text.Substring(test.LastIndexOf("/")), out result))
{
//its good
}
else
{
//its bad
}