How to parse a string into a nullable int

Glenn_Slaven_2975 0
Viewed 209823

I'm wanting to parse a string into a nullable int in C#. ie. I want to get back either the int value of the string or null if it can't be parsed.

I was kind of hoping that this would work

int? val = stringVal as int?;

But that won't work, so the way I'm doing it now is I've written this extension method

public static int? ParseNullableInt(this string value)
{
    if (value == null || value.Trim() == string.Empty)
    {
        return null;
    }
    else
    {
        try
        {
            return int.Parse(value);
        }
        catch
        {
            return null;
        }
    }
}

Is there a better way of doing this?

EDIT: Thanks for the TryParse suggestions, I did know about that, but it worked out about the same. I'm more interested in knowing if there is a built-in framework method that will parse directly into a nullable int?

nullable .net-3.5 string .net c#
22 Answers

int.TryParse is probably a tad easier:

public static int? ToNullableInt(this string s)
{
    int i;
    if (int.TryParse(s, out i)) return i;
    return null;
}

Edit @Glenn int.TryParse is "built into the framework". It and int.Parse are the way to parse strings to ints.

Matt_Hamilton_6150

You can do this in one line, using the conditional operator and the fact that you can cast null to a nullable type (two lines, if you don't have a pre-existing int you can reuse for the output of TryParse):

Pre C#7:

int tempVal;
int? val = Int32.TryParse(stringVal, out tempVal) ? tempVal : (int?)null;

With C#7's updated syntax that allows you to declare an output variable in the method call, this gets even simpler.

int? val = Int32.TryParse(stringVal, out var tempVal) ? tempVal : (int?)null;
McKenzieG1_37760

[Updated to use modern C# as per @sblom's suggestion]

I had this problem and I ended up with this (after all, an if and 2 returns is soo long-winded!):

int? ToNullableInt (string val)
    => int.TryParse (val, out var i) ? (int?) i : null;

On a more serious note, try not to mix int, which is a C# keyword, with Int32, which is a .NET Framework BCL type - although it works, it just makes code look messy.

Duckboy_27240

C# >= 7.1

var result = int.TryParse(foo, out var f) ? f : default;

See C# language versioning to ascertain what language version your project supports

user_95578520

Try this:

public static int? ParseNullableInt(this string value)
{
    int intValue;
    if (int.TryParse(value, out intValue))
        return intValue;
    return null;
}
user_5070

I'm more interested in knowing if there is a built-in framework method that will parse directly into a nullable int?

There isn't.

Orion_Edwards_2340

This solution is generic without reflection overhead.

public static Nullable<T> ParseNullable<T>(string s, Func<string, T> parser) where T : struct
{
    if (string.IsNullOrEmpty(s) || string.IsNullOrEmpty(s.Trim())) return null;
    else return parser(s);
}

static void Main(string[] args)
{
    Nullable<int> i = ParseNullable("-1", int.Parse);
    Nullable<float> dt = ParseNullable("3.14", float.Parse);
}
user_25148030

The cleaner way would be to write a separate function or extension method, but if you just want a one-liner:

string s;
int? i = s == null ? (int?)null : int.Parse(s);
user_33483260

You should never use an exception if you don't have to - the overhead is horrible.

The variations on TryParse solve the problem - if you want to get creative (to make your code look more elegant) you could probably do something with an extension method in 3.5 but the code would be more or less the same.

Murph_10700

I realise this is an old topic, but can't you simply:

(Nullable<int>)int.Parse(stringVal);

?

user_14150410
Related