How to use int.TryParse with nullable int? [duplicate]

Answer 1

You could also make an extension method for this purpose;

public static bool TryParse(this object value, out int? parsed)
{
    parsed = null;
    try
    {
        if (value == null)
            return true;

        int parsedValue;
        parsed = int.TryParse(value.ToString(), out parsedValue) ? (int?)parsedValue : null;
        return true;
    }
    catch (Exception)
    {
        return false;
    }
}

I've made this an extension on the object type, but it could equally well be on string. Personally I like these parser-extensions to be available on any object hence the extension on object instead of string.

Example of use:

[TestCase("1", 1)]
[TestCase("0", 0)]
[TestCase("-1", -1)]
[TestCase("2147483647", int.MaxValue)]
[TestCase("2147483648", null)]
[TestCase("-2147483648", int.MinValue)]
[TestCase("-2147483649", null)]
[TestCase("1.2", null)]
[TestCase("1 1", null)]
[TestCase("", null)]
[TestCase(null, null)]
[TestCase("not an int value", null)]
public void Should_parse_input_as_nullable_int(object input, int? expectedResult)
{
    int? parsedValue;

    bool parsingWasSuccessfull = input.TryParse(out parsedValue);

    Assert.That(parsingWasSuccessfull);
    Assert.That(parsedValue, Is.EqualTo(expectedResult));
}

The downside would be that this breaks with the frameworks syntax for parsing values;

int.TryParse(input, out output))

But I like the shorter version of it (whether it's more readable or not might be subject to discussion);

input.TryParse(out output)

Answer 2

You can create a helper method to parse a nullable value.

Example Usage:

int? intVal;
if( !NullableInt.TryParse( "42", out intVal ) )
{
    break;
}

Helper Method:

public static class NullableInt
{
    public static bool TryParse( string text, out int? outValue )
    {
        int parsedValue;
        bool success = int.TryParse( text, out parsedValue );
        outValue = success ? (int?)parsedValue : null;
        return success;
    }
}

Answer 3

You can't do this without using another variable, unfortunately - because the type of out arguments has to match the parameter exactly.

Like Daniel's code, but fixed in terms of the second argument, trimming, and avoiding comparisons with Boolean constants:

int tmp;
if (!int.TryParse(strValue.Trim(), out tmp))
{
    break;
}
intVal = tmp;

Answer 4

Here's an option for a nullable int with TryParse

public int? TryParseNullable(string val)
{
    int outValue;
    return int.TryParse(val, out outValue) ? (int?)outValue : null;
}

Answer 5

Could not prevent myself to produce a generic version. Usage below.

    public class NullableHelper
    {
        public delegate bool TryDelegate<T>(string s, out T result);

        public static bool TryParseNullable<T>(string s, out T? result, TryDelegate<T> tryDelegate) where T : struct
        {
            if (s == null)
            {
                result = null;
                return true;
            }

            T temp;
            bool success = tryDelegate(s, out temp);
            result = temp;
            return success;
        }

        public static T? ParseNullable<T>(string s, TryDelegate<T> tryDelegate) where T : struct
        {
            if (s == null)
            {
                return null;
            }

            T temp;
            return tryDelegate(s, out temp)
                       ? (T?)temp
                       : null;
        } 
    }


bool? answer = NullableHelper.ParseNullable<bool>(answerAsString, Boolean.TryParse);