One thing that has bothered me about C# since its release was the lack of a generic IsNumeric function. I know it is difficult to generate a one-stop solution to detrmine if a value is numeric.
I have used the following solution in the past, but it is not the best practice because I am generating an exception to determine if the value is IsNumeric:
public bool IsNumeric(string input)
{
try
{
int.Parse(input);
return true;
}
catch
{
return false;
}
}
Is this still the best way to approach this problem or is there a more efficient way to determine if a value is numeric in C#?
Try this:
int temp;
return int.TryParse(input, out temp);
Of course, the behavior will be different from Visual Basic IsNumeric. If you want that behavior, you can add a reference to "Microsoft.VisualBasic" assembly and call the Microsoft.VisualBasic.Information.IsNumeric function directly.
You can use extension methods to extend the String type to include IsInteger:
namespace ExtensionMethods
{
public static class MyExtensions
{
public static bool IsInteger(this String input)
{
int temp;
return int.TryParse(input, out temp);
}
}
}
Rather than using int.Parse, you can use int.TryParse and avoid the exception.
Something like this
public static bool IsNumeric(string input)
{
int dummy;
return int.TryParse(input, out dummy);
}
More generically you might want to look at double.TryParse.
One thing you should also consider is the potential of handling numeric string for different cultures. For example Greek (el-GR) uses , as a decimal separator while the UK (en-GB) uses a .. So the string "1,000" will either be 1000 or 1 depending on the current culture. Given this, you might consider providing overloads for IsNumeric that support passing the intended culture, number format etc. Take a look at the 2 overloads for double.TryParse.
I've used the following extension method before, if it helps at all:
public static int? AsNumeric(this string source)
{
int result;
return Int32.TryParse(source, out result) ? result : (int?)null;
}
Then you can use .HasValue for the bool you have now, or .Value for the value, but convert just once...just throwing it out there, not sure what situation you're using it for afterwards.
If you use Int32.TryParse then you don't need to wrap the call in a TryCatch block, but otherwise, yes that is the approach to take.
Not exactly crazy about this approach, but you can just call the vb.net isNumeric function from C# by adding a reference to the Microsoft.VisualBasic.dll library...
bool x= Microsoft.VisualBasic.Information.IsNumeric("123");
The other approaches given are superior, but wanted to add this for the sake of completeness.
Lot's of TryParse answers. Here's something a bit different using Char.IsNumber():
public bool IsNumeric(string s)
{
for (int i = 0; i < s.Length; i++)
{
if (char.IsNumber(s, i) == false)
{
return false;
}
}
return true;
}
Take a look on the following answer:
What is the C# equivalent of NaN or IsNumeric?
Double.TryParse takes care of all numeric values and not only ints.
Another option - LINQ!
public static class StringExtensions
{
public static bool IsDigits(this String text)
{
return !text.Any(c => !char.IsDigit(c));
}
}
Note that this assumes you only want digits 0-9. If you want to accept decimal point, sign, exponent, etc, then repalce IsDigit() with IsNumber().
I've been using the following small code snippet for years as a pure C# IsNumeric function.
Granted, it's not exactly the same as the Microsoft.VisualBasic library's IsNumeric function as that (if you look at the decompiled code) involves lots of type checking and usage of the IConvertible interface, however this small function has worked well for me.
Note also that this function uses double.TryParse rather than int.TryParse to allow both integer numbers (including long's) as well as floating point numbers to be parsed. Also note that this function specifically asserts an InvariantCulture when parsing (for example) floating point numbers, so will correctly identify both 123.00 and 123,00 (note the comma and decimal point separators) as floating point numbers.
using System;
using System.Globalization;
namespace MyNumberFunctions
{
public static class NumberFunctions
{
public static bool IsNumeric(this object expression)
{
if (expression == null)
{
return false;
}
double number;
return Double.TryParse(Convert.ToString(expression, CultureInfo.InvariantCulture), NumberStyles.Any, NumberFormatInfo.InvariantInfo, out number);
}
}
}
Usage is incredibly simple, since this is implemented as an extension method:
string myNumberToParse = "123.00";
bool isThisNumeric = myNumberToParse.IsNumeric();
public bool IsNumeric(string input)
{
int result;
return Int32.TryParse(input,out result);
}
try this:
public static bool IsNumeric(object o)
{
const NumberStyles sty = NumberStyles.Any;
double d;
return (o != null && Double.TryParse(o.ToString(), sty, null, out d));
}
You can still use the Visual Basic function in C#. The only thing you have to do is just follow my instructions shown below:
Add the reference to the Visual Basic Library by right clicking on your project and selecting "Add Reference":
Then import it in your class as shown below:
using Microsoft.VisualBasic;
Next use it wherever you want as shown below:
if (!Information.IsNumeric(softwareVersion))
{
throw new DataException(string.Format("[{0}] is an invalid App Version! Only numeric values are supported at this time.", softwareVersion));
}
Hope, this helps and good luck!
Related
I'm wondering what the correct way to compare two characters ignoring case that will work for all cultures. Also, is Comparer<char>.Default the best way to test two characters without ignoring case? Does this work for surrogate-pairs?
EDIT: Added sample IComparer<char> implementation
If this helps anyone this is what I've decided to use
public class CaseInsensitiveCharComparer : IComparer<char> {
private readonly System.Globalization.CultureInfo ci;
public CaseInsensitiveCharComparer(System.Globalization.CultureInfo ci) {
this.ci = ci;
}
public CaseInsensitiveCharComparer()
: this(System.Globalization.CultureInfo.CurrentCulture) { }
public int Compare(char x, char y) {
return Char.ToUpper(x, ci) - Char.ToUpper(y, ci);
}
}
// Prints 3
Console.WriteLine("This is a test".CountChars('t', new CaseInsensitiveCharComparer()));
It depends on what you mean by "work for all cultures". Would you want "i" and "I" to be equal even in Turkey?
You could use:
bool equal = char.ToUpperInvariant(x) == char.ToUpperInvariant(y);
... but I'm not sure whether that "works" according to all cultures by your understanding of "works".
Of course you could convert both characters to strings and then perform whatever comparison you want on the strings. Somewhat less efficient, but it does give you all the range of comparisons available in the framework:
bool equal = x.ToString().Equals(y.ToString(),
StringComparison.InvariantCultureIgnoreCase);
For surrogate pairs, a Comparer<char> isn't going to be feasible anyway, because you don't have a single char. You could create a Comparer<int> though.
As I understand it, there isn't really a way that will "work for all cultures". Either you want to compare characters for some kind of internal, non-displayed-to-the-user reason (in which case you should use the InvariantCulture), or you want to use the CurrentCulture of the user. Obviously, using the user's current culture will mean that you will get different results in different locales, but they will be consistent with what your users in those locales will expect.
Without knowing more about WHY you are comparing two characters, I can't really advise you on which one you should be using.
I would recommend comparing uppercase, and if they don't match then comparing lowercase, just in case the locale's uppercasing and lowercasing logic behave slightly different.
Addendum
For example,
int CompareChar(char c1, char c2)
{
int dif;
dif = char.ToUpper(c1) - char.ToUpper(c2);
if (diff != 0)
dif = char.ToLower(c1) - char.ToLower(c2);
return dif;
}
What I was thinking that would be available within the runtime is something like the following
public class CaseInsensitiveCharComparer : IComparer<char> {
private readonly System.Globalization.CultureInfo ci;
public CaseInsensitiveCharComparer(System.Globalization.CultureInfo ci) {
this.ci = ci;
}
public CaseInsensitiveCharComparer()
: this(System.Globalization.CultureInfo.CurrentCulture) { }
public int Compare(char x, char y) {
return Char.ToUpper(x, ci) - Char.ToUpper(y, ci);
}
}
// Prints 3
Console.WriteLine("This is a test".CountChars('t', new CaseInsensitiveCharComparer()));
You could try:
class Test{
static int Compare(char t, char p){
return string.Compare(t.ToString(), p.ToString(), StringComparison.CurrentCultureIgnoreCase);
}
}
But I doubt this is the "optimal" way to do it, but I'm not all of the cases you need to be checking...
string.Compare("string a","STRING A",true)
It will work for every string
I know this is an old post, but things have changed since then.
The question above can be answered by using an extension. This would extend the char.Equals to allow for locality and case insensitivity.
In an extension class, add something such as:
internal static Boolean Equals(this Char src, Char ch, StringComparison comp)
{
Return $"{src}".Equals($"{ch}", comp);
}
I'm currently at work, so can't check this, but it should work.
Andy
You can provide last argument as true for caseInsensetive match
string.Compare(lowerCase, upperCase, true);
In C# Convert.ToInt32() and any method of Convert class can handle null values but all these method not handling "" as input. Throws an error "input string not in correct format"
Is there any way to handle/Convert "" to its specific value? like
Convert.ToInt32("") convert to 0
Convert.ToDecimal("") convert to 0.0
with out using if conditions
Thanks.
The POD classes in C# have a method just for this reason:
Int32.TryParse
You could even write an extension method to make this easier for you:
public static class Extensions {
public static decimal MyDecimalParse(this string val) {
decimal ret = decimal.Zero;
decimal.TryParse(val, out ret);
return ret;
}
} // eo class extension
Try int.TryParse
int i;
bool b = int.TryParse("", out i);
Console.WriteLine(b);
There isn't anything inherent in the frameworks that do this for you. It probably doesn't make sense for the entire community to understand "" as defaulting to 0 or 0.0 as you would want. I would recommend writing your own method that does what you specifically want.
Something to the effect of:
public class MyConvert
{
public static int ToInt32(string input)
{
return String.IsNullOrEmpty(input) ? 0 : Convert.ToInt32(input);
}
}
I realize you don't want to do the if check but you will have to check it one way or another (either by checking .IsNullOrEmpty or .TryParse), so abstracting it into your own convert method at least means you don't have to do it every time.
I find myself often needing to use int.TryParse() to test if a value is an integer. However, when using TryParse, I have to pass a reference variable to the function. So I find myself always needing to create a temp int to be passed in. Usually it looks something like:
int my_temp_integer;
int.TryParse(potential_integer, my_temp_integer);
I find this to be quite cumbersome considering that all I want is a simple true/false response, and I don't care about the actual parsed result. Is there a better way to approach this? Why isn't there an overloaded function where I can just pass the value I want to test and get a true/false response?
Thanks.
you could write an extension method:
public static bool IsInt(this string pString)
{
int value;
return int.TryParse(pString, out value);
}
then your example becomes:
potential_integer.IsInt();
EDIT:
Lately I have been using a generic form of this.
public delegate bool TryParser<T>(string pString, out T pResult);
public static bool Is<T>(this string pString, TryParser<T> pTryParser)
{
T val;
return pTryParser(pString, out val);
}
Can then use it as follows; it's not perfect, but it's more concise than anything I've found:
"1234".Is<int>(int.TryParse); // true
"asdf123".Is<int>(int.TryParse); // false
"1.2345".Is<float>(float.TryParse); // true
"1000".Is<byte>(byte.TryParse); // false
Theoretically, this would also work with custom TryParse methods, as long as you followed the same pattern as the official ones.
Update: If you maintain a static dictionary of TryParse methods by type, you can avoid having to ever directly pass the method. The dictionary can even be populated as needed with reflection.
A simple solution is to create an extension method.
public static class StringExtensions {
public static bool IsInt(this string s) {
int i; return Int.TryParse(s, out i);
}
}
Then you just use it as so:
string s = "123";
if (s.IsInt())
// do something.
if you don't want to actually convert the string, only test it, then you can use Regex
something kinda like this (you may need to adjust this to fit your needs):
public bool IsInt(this string inputData)
{
Regex isNumber = new Regex(#"^\d+$");
Match m = isNumber.Match(inputData);
return m.Success;
}
You could use
bool isInt = str.TrimEnd( new char[] {'0','1','2','3','4','5','6','7','8','9'})
.Length == 0;
A shorter alternative to Muad'Dib above:
bool IsInt(string input)
{
return new System.Text.RegularExpressions.Regex(#"^\d$").IsMatch(input);
}
/Hans
I'm wondering what the correct way to compare two characters ignoring case that will work for all cultures. Also, is Comparer<char>.Default the best way to test two characters without ignoring case? Does this work for surrogate-pairs?
EDIT: Added sample IComparer<char> implementation
If this helps anyone this is what I've decided to use
public class CaseInsensitiveCharComparer : IComparer<char> {
private readonly System.Globalization.CultureInfo ci;
public CaseInsensitiveCharComparer(System.Globalization.CultureInfo ci) {
this.ci = ci;
}
public CaseInsensitiveCharComparer()
: this(System.Globalization.CultureInfo.CurrentCulture) { }
public int Compare(char x, char y) {
return Char.ToUpper(x, ci) - Char.ToUpper(y, ci);
}
}
// Prints 3
Console.WriteLine("This is a test".CountChars('t', new CaseInsensitiveCharComparer()));
It depends on what you mean by "work for all cultures". Would you want "i" and "I" to be equal even in Turkey?
You could use:
bool equal = char.ToUpperInvariant(x) == char.ToUpperInvariant(y);
... but I'm not sure whether that "works" according to all cultures by your understanding of "works".
Of course you could convert both characters to strings and then perform whatever comparison you want on the strings. Somewhat less efficient, but it does give you all the range of comparisons available in the framework:
bool equal = x.ToString().Equals(y.ToString(),
StringComparison.InvariantCultureIgnoreCase);
For surrogate pairs, a Comparer<char> isn't going to be feasible anyway, because you don't have a single char. You could create a Comparer<int> though.
As I understand it, there isn't really a way that will "work for all cultures". Either you want to compare characters for some kind of internal, non-displayed-to-the-user reason (in which case you should use the InvariantCulture), or you want to use the CurrentCulture of the user. Obviously, using the user's current culture will mean that you will get different results in different locales, but they will be consistent with what your users in those locales will expect.
Without knowing more about WHY you are comparing two characters, I can't really advise you on which one you should be using.
I would recommend comparing uppercase, and if they don't match then comparing lowercase, just in case the locale's uppercasing and lowercasing logic behave slightly different.
Addendum
For example,
int CompareChar(char c1, char c2)
{
int dif;
dif = char.ToUpper(c1) - char.ToUpper(c2);
if (diff != 0)
dif = char.ToLower(c1) - char.ToLower(c2);
return dif;
}
What I was thinking that would be available within the runtime is something like the following
public class CaseInsensitiveCharComparer : IComparer<char> {
private readonly System.Globalization.CultureInfo ci;
public CaseInsensitiveCharComparer(System.Globalization.CultureInfo ci) {
this.ci = ci;
}
public CaseInsensitiveCharComparer()
: this(System.Globalization.CultureInfo.CurrentCulture) { }
public int Compare(char x, char y) {
return Char.ToUpper(x, ci) - Char.ToUpper(y, ci);
}
}
// Prints 3
Console.WriteLine("This is a test".CountChars('t', new CaseInsensitiveCharComparer()));
You could try:
class Test{
static int Compare(char t, char p){
return string.Compare(t.ToString(), p.ToString(), StringComparison.CurrentCultureIgnoreCase);
}
}
But I doubt this is the "optimal" way to do it, but I'm not all of the cases you need to be checking...
string.Compare("string a","STRING A",true)
It will work for every string
I know this is an old post, but things have changed since then.
The question above can be answered by using an extension. This would extend the char.Equals to allow for locality and case insensitivity.
In an extension class, add something such as:
internal static Boolean Equals(this Char src, Char ch, StringComparison comp)
{
Return $"{src}".Equals($"{ch}", comp);
}
I'm currently at work, so can't check this, but it should work.
Andy
You can provide last argument as true for caseInsensetive match
string.Compare(lowerCase, upperCase, true);
Consider the need for a function in C# that will test whether a string is a numeric value.
The requirements:
must return a boolean.
function should be able to allow for whole numbers, decimals, and negatives.
assume no using Microsoft.VisualBasic to call into IsNumeric(). Here's a case of reinventing the wheel, but the exercise is good.
Current implementation:
//determine whether the input value is a number
public static bool IsNumeric(string someValue)
{
Regex isNumber = new Regex(#"^\d+$");
try
{
Match m = isNumber.Match(someValue);
return m.Success;
}
catch (FormatException)
{return false;}
}
Question: how can this be improved so that the regex would match negatives and decimals? Any radical improvements that you'd make?
Just off of the top of my head - why not just use double.TryParse ? I mean, unless you really want a regexp solution - which I'm not sure you really need in this case :)
Can you just use .TryParse?
int x;
double y;
string spork = "-3.14";
if (int.TryParse(spork, out x))
Console.WriteLine("Yay it's an int (boy)!");
if (double.TryParse(spork, out y))
Console.WriteLine("Yay it's an double (girl)!");
Regex isNumber = new Regex(#"^[-+]?(\d*\.)?\d+$");
Updated to allow either + or - in front of the number.
Edit: Your try block isn't doing anything as none of the methods within it actually throw a FormatException. The entire method could be written:
// Determine whether the input value is a number
public static bool IsNumeric(string someValue)
{
return new Regex(#"^[-+]?(\d*\.)?\d+$").IsMatch(someValue);
}
Well, for negatives you'd need to include an optional minus sign at the start:
^-?\d+$
For decimals you'd need to account for a decimal point:
^-?\d*\.?\d*$
And possible exponential notation:
^-?\d*\.?\d*(e\d+)?$
I can't say that I would use regular expressions to check if a string is a numeric value. Slow and heavy for such a simple process. I would simply run over the string one character at a time until I enter an invalid state:
public static bool IsNumeric(string value)
{
bool isNumber = true;
bool afterDecimal = false;
for (int i=0; i<value.Length; i++)
{
char c = value[i];
if (c == '-' && i == 0) continue;
if (Char.IsDigit(c))
{
continue;
}
if (c == '.' && !afterDecimal)
{
afterDecimal = true;
continue;
}
isNumber = false;
break;
}
return isNumber;
}
The above example is simple, and should get the job done for most numbers. It is not culturally sensitive, however, but it should be strait-forward enough to make it culturally sensitive.
Also, make sure the resulting code passes the Turkey Test:
http://www.moserware.com/2008/02/does-your-code-pass-turkey-test.html
Unless you really want to use regex, Noldorin posted a nice extension method in another Q&A.
Update
As Patrick rightly pointed out, the link points to an extension method that check whether the object is a numeric type or not, not whether it represents a numeric value. Then using double.TryParse as suggested by Saulius and yodaj007 is probably the best choice, handling all sorts of quirks with different decimal separators, thousand separators and so on. Just wrap it up in a nice extension method:
public static bool IsNumeric(this string value)
{
double temp;
return double.TryParse(value.ToString(), out temp);
}
...and fire away:
string someValue = "89.9";
if (someValue.IsNumeric()) // will be true in the US, but not in Sweden
{
// wow, it's a number!
]