I am writing a program in C#, and I want to catch exceptions caused by converting "" (null) to int. What is the exception's name?
EDIT:
I'm not sure I can show the full code... But I'm sure you don't need the full code, so:
int num1 = Int32.Parse(number1.Text);
int num2 = Int32.Parse(number2.Text);
If you can avoid it, do not code by exception!
The exception name you are looking for is called a FormatException.
However, it would be smarter to first do a TryParse on the object you are attempting to parse, e.g.
int value;
if(!int.TryParse("1", out value))
{
// You caught it without throwing an exception.
}
You are going to get a FormatException if a parse fails. Why not use int.TryParse instead?
As a side note, a simple way to find out the exception is to run it. When you encounter the error, it'll give you the exception name.
Let's have a look at the documentation (which is a much cleaner solution that "trying it out"):
public static int Parse(string s)
[...]
Exceptions:
ArgumentNullException: s is null.
FormatException: s is not in the correct format.
This should answer your question. As others have already mentioned, maybe you are asking the wrong question and want to use Int32.TryParse instead.
Depends on what you're using to do the conversion. For example, int.Parse will throw ArgumentNullException, FormatException, or OverflowException. Odds are it's ArgumentNullException you're looking for, but if that's an empty string rather than a null reference, it's probably going to be FormatException
When the exception fires you can see it's type. The smart thing to do is handle that case and display a graceful message to your user if possible.
You're probably looking to get a System.InvalidCastException, although I think that'll depend on how you try to perform the conversion.
That said, wouldn't it be quicker/easier to simply write the code and try it yourself? Particularly as you haven't specified how you'll be performing the conversion.
Just try it. This code:
int.Parse("");
Throws a FormatException.
Exceptions are expensive. You should use int.TryParse. It will return the boolean false if the conversion fails.
Convert.ToInt32 does not throw a format exception ("input string is not in the correct format") on a null string. You can use that if it is acceptable for the result to be a 0 for a null string. (still pukes on empty string though)
string s = null;
int i = Convert.ToInt32(s);
But if you expect a number to be in the box, you should either use TryParse (as was suggested) or a Validator of some kind to inform the user that they need to enter a number.
Related
What is the difference between Parse() and TryParse()?
int number = int.Parse(textBoxNumber.Text);
// The Try-Parse Method
int.TryParse(textBoxNumber.Text, out number);
Is there some form of error-checking like a Try-Catch Block?
Parse throws an exception if it cannot parse the value, whereas TryParse returns a bool indicating whether it succeeded.
TryParse does not just try/catch internally - the whole point of it is that it is implemented without exceptions so that it is fast. In fact the way it is most likely implemented is that internally the Parse method will call TryParse and then throw an exception if it returns false.
In a nutshell, use Parse if you are sure the value will be valid; otherwise use TryParse.
If the string can not be converted to an integer, then
int.Parse() will throw an exception
int.TryParse() will return false (but not throw an exception)
The TryParse method allows you to test whether something is parseable. If you try Parse as in the first instance with an invalid int, you'll get an exception while in the TryParse, it returns a boolean letting you know whether the parse succeeded or not.
As a footnote, passing in null to most TryParse methods will throw an exception.
TryParse and the Exception Tax
Parse throws an exception if the conversion from a string to the specified datatype fails, whereas TryParse explicitly avoids throwing an exception.
TryParse does not return the value, it returns a status code to indicate whether the parse succeeded (and doesn't throw an exception).
For the record, I am testing two codes: That simply try to convert from a string to a number and if it fail then assign number to zero.
if (!Int32.TryParse(txt,out tmpint)) {
tmpint = 0;
}
and:
try {
tmpint = Convert.ToInt32(txt);
} catch (Exception) {
tmpint = 0;
}
For c#, the best option is to use tryparse because try&Catch alternative thrown the exception
A first chance exception of type 'System.FormatException' occurred in mscorlib.dll
That it is painful slow and undesirable, however, the code does not stop unless Debug's exception are settled for stop with it.
I know its a very old post but thought of sharing few more details on Parse vs TryParse.
I had a scenario where DateTime needs to be converted to String and if datevalue null or string.empty we were facing an exception. In order to overcome this, we have replaced Parse with TryParse and will get default date.
Old Code:
dTest[i].StartDate = DateTime.Parse(StartDate).ToString("MM/dd/yyyy");
dTest[i].EndDate = DateTime.Parse(EndDate).ToString("MM/dd/yyyy");
New Code:
DateTime startDate = default(DateTime);
DateTime endDate=default(DateTime);
DateTime.TryParse(dPolicyPaidHistories[i].StartDate, out startDate);
DateTime.TryParse(dPolicyPaidHistories[i].EndDate, out endDate);
Have to declare another variable and used as Out for TryParse.
double.Parse("-"); raises an exception, while
double.TryParse("-", out parsed); parses to 0
so I guess TryParse does more complex conversions.
Getting the error, when trying to execute this line:
spellPrefabs[Int32.Parse(spell.spellName)]
spell.spellName is a string equal to "0"
Can't get it, why is it not working. Any ideas? Am I just dumb and miss something obvious?
Double-check that spell.spellName.Length is 1 and (int)spell.spellName[0] is 0x30. The debugger display might not show all the characters that are actually in the string.
If the string is from user input it might be a good idea to be prepared for such incorrectly formed input by either catching the exception or using int.TryParse.
I am trying to parse some string to a double value, using this parse method overload:
double.Parse("198.222213745118", CultureInfo.CurrentUICulture);
the CultureInfo.CurrentUICulture is fr-FR.
but this is throwing an exception of type FormatException.
What can be the reason?
French (i.e. fr-FR) use a comma to denote the start of the decimal part, not a period. They use a period to separate thousands.
I know this question is old but my answer might help someone else.
So this is the answer:
double.Parse("198.222213745118", System.Globalization.NumberStyles.AllowDecimalPoint, System.Globalization.NumberFormatInfo.InvariantInfo);
instead of
double.Parse("198.222213745118", CultureInfo.CurrentUICulture);
I suggest using the Double.TryParse rather than the .Parse as it is safer to use and makes sure you dont get any exception on parsing.
Here is a Code for you to use,
double answer = -1;
Double.TryParse("Value", out answer);
Now all you have to do is do a conditional statement that'll check if it indeed parsed' the string.
I have a text box named textBox1, and In a certain case, I want to convert the string in the textbox to an integer for later use as an integer.
It's throwing an error that I can't even understand. Here is a screenshot:
(Per Request) The code is:
this.textBox1.Text = string.Concat(Int.Where(c => Char.IsNumber(c)));
this.textBox1.Text = Convert.ToInt32(this.textBox1.Text);
I would really appreciate it if you could give me an answer or fix to my code, and explain why it doesn't/does work.
Convert.ToInt32 will, by design, return an integer, not a string.
If you're just storing the result back into the text box, there's no reason at all to convert it to a number only to convert it back to a string.
This would really only be useful if you wanted to do:
int value = Convert.ToInt32(this.textBox1.Text);
That being said, you might want to use Int32.TryParse instead. This allows you to check for formatting errors instead of having exceptions raised if the user types inappropriate values.
What is the difference between Parse() and TryParse()?
int number = int.Parse(textBoxNumber.Text);
// The Try-Parse Method
int.TryParse(textBoxNumber.Text, out number);
Is there some form of error-checking like a Try-Catch Block?
Parse throws an exception if it cannot parse the value, whereas TryParse returns a bool indicating whether it succeeded.
TryParse does not just try/catch internally - the whole point of it is that it is implemented without exceptions so that it is fast. In fact the way it is most likely implemented is that internally the Parse method will call TryParse and then throw an exception if it returns false.
In a nutshell, use Parse if you are sure the value will be valid; otherwise use TryParse.
If the string can not be converted to an integer, then
int.Parse() will throw an exception
int.TryParse() will return false (but not throw an exception)
The TryParse method allows you to test whether something is parseable. If you try Parse as in the first instance with an invalid int, you'll get an exception while in the TryParse, it returns a boolean letting you know whether the parse succeeded or not.
As a footnote, passing in null to most TryParse methods will throw an exception.
TryParse and the Exception Tax
Parse throws an exception if the conversion from a string to the specified datatype fails, whereas TryParse explicitly avoids throwing an exception.
TryParse does not return the value, it returns a status code to indicate whether the parse succeeded (and doesn't throw an exception).
For the record, I am testing two codes: That simply try to convert from a string to a number and if it fail then assign number to zero.
if (!Int32.TryParse(txt,out tmpint)) {
tmpint = 0;
}
and:
try {
tmpint = Convert.ToInt32(txt);
} catch (Exception) {
tmpint = 0;
}
For c#, the best option is to use tryparse because try&Catch alternative thrown the exception
A first chance exception of type 'System.FormatException' occurred in mscorlib.dll
That it is painful slow and undesirable, however, the code does not stop unless Debug's exception are settled for stop with it.
I know its a very old post but thought of sharing few more details on Parse vs TryParse.
I had a scenario where DateTime needs to be converted to String and if datevalue null or string.empty we were facing an exception. In order to overcome this, we have replaced Parse with TryParse and will get default date.
Old Code:
dTest[i].StartDate = DateTime.Parse(StartDate).ToString("MM/dd/yyyy");
dTest[i].EndDate = DateTime.Parse(EndDate).ToString("MM/dd/yyyy");
New Code:
DateTime startDate = default(DateTime);
DateTime endDate=default(DateTime);
DateTime.TryParse(dPolicyPaidHistories[i].StartDate, out startDate);
DateTime.TryParse(dPolicyPaidHistories[i].EndDate, out endDate);
Have to declare another variable and used as Out for TryParse.
double.Parse("-"); raises an exception, while
double.TryParse("-", out parsed); parses to 0
so I guess TryParse does more complex conversions.