I want to run a check on a String right before I append it to a StringBuilder to make sure only numeric characters are in the string. What's a simple way to do that?
9 Answers
Use Integer.TryParse() it will return true if there are only digits in the string. Int32 max value is 2,147,483,647 so if your value is less then that then your fine. http://msdn.microsoft.com/en-us/library/f02979c7.aspx
You can also use Double.TryParse() which has a max value of 1.7976931348623157E+308 but it will allow a decimal point.
If your looking to get the value that isnt an integer you can always go through the string one at a time
string test = "1112003212g1232";
int result;
bool append=true;
for (int i = 0; i < test.Length-1; i++)
{
if(!Int32.TryParse(test.Substring(i,i+1),out result))
{
//Not an integer
append = false;
}
}
If append stays true then the string is an integer. Probably a more slick way of doing this but this should work.
5 Comments
AllenG
As long as the string isn't larger than the max Int32.
Rockcoder
That won't work if the string is too long resulting in the integer overflow
Scott
Pretty much I just want to make sure a string only has numeric characters, and IF it doesn't, I need to find the location in that string where the non-numeric character is located, and see what the value is
Gage
Yes I realize thats C#, same basic idea though
tryman
This will fail if a string represents a number below zero: eg. -1 This will be parsed as a number but what you want to actually check is if the string is digits-only. For finite accuracy and assumptions on string length, at least check if it's negative.
Coding in VB.Net to check whether a string contains only numeric values or not.
If IsNumeric("your_text") Then
MessageBox.Show("yes")
Else
MessageBox.Show("no")
End If
Comments
Use regular expressions:
Dim reg as New RegEx("^\d$")
If reg.IsMatch(myStringToTest) Then
' Numeric
Else
' Not
End If
UPDATE:
You could also use linq to accomplish the same task if you're doing it in VB.Net 2008/2010.
Dim isNumeric as Boolean = False
Dim stringQuery = From c In myStringToTest
Where Char.IsDigit(c)
Select c
If stringQuery.Count <> myStringToTest.Length Then isNumeric = False
1 Comment
knslyr
Regular Expressions is the more elegant solution IMHO. We use RE for most of our input validation and data scrubbing.
If you do not wish to use RegEx, a simple check on each character with char.IsNumber works.
You can combine it with the All extension method (in C#, I don't know how to write it in VB.net):
string value = "78645655";
bool isValid = value.All(char.IsNumber);
Check out other char method, like IsDigit.
answered Jul 30, 2010 at 19:16
Pierre-Alain Vigeant
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1 Comment
Jeff B
Unfortunately VB won't let you write something as elegant. You'd end up with
value.All(Function(c) Char.IsNumber(c))2 other compact solutions :
Without LINQ :
Dim foo As String = "10004"
Array.Exists(foo.ToCharArray, Function(c As Char) Not Char.IsNumber(c))
With LINQ (just VB.Net equivalent of the C# version in another answer) :
foo.All(Function(c As Char) Char.IsNumber(c))
Comments
Negative values haven't been mentioned, which Integer.TryParse would accept.
I prefer UInteger.TryParse which will reject a negative number. However, there is an additional check required in case the value starts with "+":
Dim test As String = "1444"
Dim outTest As UInteger
If Not test.StartsWith("+") AndAlso UInteger.TryParse(test, outTest) Then
MessageBox.Show("It's just digits!")
End If
or ULong.TryParse for a larger number.
Comments
You can use regular expression or Integer.TryParse and I prefer the regular expression check
Comments
Presuming you're looking at relatively short strings which will never have a number greater than the Max Int32 value, use Gage's solution. If it's a variable length and sometimes you could overflow, use Regex (System.Text.RegularExpressions)
The regex for checking against just numbers is fairly routine: ^[0-9]+$
Check here for a very good explanation of Regex.
0x87valid?