I used TryParse to parse a string to number. I need a solution to initialize out variable with default value, So when TryParse fails to convert I get my default value.
Here is the code :
long.TryParse(input.Code, out long Code = 123);
//Error CS1525 Invalid expression term '='
I want to strictly to use C#7 out variables standard.
Whilst the out parameter itself cannot take a default value, you can achieve what you want to do with a single expression in C# 7. You simply combine the out parameter with a ternary expression:
var code = long.TryParse(input.Code, out long result) ? result : 123;
You can't do it... The .NET runtime doesn't know anything of "success" or "failure" of long.TryParse. It only knows that TryParse has a bool return value and that after TryParse finishes, the out variable will be initialized. There is no necessary correlation between true and "there is a good value in result" and false and "there is no good value in result".
To make it clear, you could have:
static bool NotTryParse(string s, out long result)
{
return !long.TryParse(s, out result);
}
And now? When should your default value be used?
Related
Why can't I add a variable value into a string using this code:
throw new ArgumentOutOfRangeException("Any Opening Type besides 'None', should have a minimum width value of 50. Your inputed value = {0}",value);
The error I get is: "CS1503: Argument 2: Cannot convert from 'int' to 'System.Exception?'"
But when I use this code it works fine:
throw new ArgumentOutOfRangeException($"Any Opening Type besides 'None', should have a minimum width value of 50. Your inputed value = {value}");
Can somebody help me understand why? As far as I know these two ways of doing it should result with the same end. I don't understand why it would be converting, shouldn't I then get the same error if I use a console.WriteLine method? What makes this special?
The first syntax only works for methods that use format strings. Some methods, like Console.WriteLine, have an overload that takes a format string as the first argument and any number of objects as a subsequent arguments array, so you're probably used to it working the same as when you use string interpolation syntax ($"...").
Most exception constructors don't follow that pattern, so you'll have to build your own string to pass in as their message argument. String interpolation syntax will do that for you automatically, as you've discovered. Or you can call string.Format explicitly:
throw new ArgumentOutOfRangeException(
string.Format(
"Any Opening Type besides 'None', should have a minimum width value of 50. Your inputed value = {0}",
value));
You should look at the documentation for the constructors of ArgumentOutOfRangeException. The parameters you provide do not match any of constructor parameter types so it throws an exception.
Instead you should format the string using String.Format() like:
throw new ArgumentOutOfRangeException(String.Format("Any Opening Type besides 'None', should have a minimum width value of 50. Your inputed value = {0}",value));
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.
What does this line of code do? I'm relatively new to C# and I've been trying to figure it out by reading about TryParse and Request.Form, however, I think a more comprehensive explanation would help me.
int.TryParse(Request.Form["yearhidden"], out year);
Request.Form provides the form element posted to the HTTP request.
int.TryParse attempts to take this value and convert it to an integer.
In this case, you're taking the "yearhidden" form element's value, and attempting to convert it to an integer, which gets set in the year variable.
Note that you'd typically check the return value of int.TryParse, and handle the case where a non-numeric value was passed into the yearhidden variable.
TryParse is taking the value from Request.Form["yearhidden"]
Request.Form["yearhidden"] is a form field in your html called yearhidden.
TryParse then attempts to parse it into an integer value. It returns True if it was successful, False if not.
The value is stored in the variable year
int.TryParse returns a boolean that represents whether or not the method was able to parse the first parameter, Request.Form["yearhidden"], into an integer.
If it is able to successfully parse the value, the value of the second parameter, year, will be set to the value.
Request.Form contains all of the information within an html form element that was sent in a given request.
out is a keyword that forces arguments to be passed by reference.
http://msdn.microsoft.com/en-us/library/t3c3bfhx(v=vs.80).aspx
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!
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.