C# – How to convert C# nullable int to int

cnullable

How do I convert a nullable int to an int? Suppose I have 2 type of int as below:

int? v1;  
int v2;

I want to assign v1's value to v2. v2 = v1; will cause an error. How do I convert v1 to v2?

Best Answer

The other answers so far are all correct; I just wanted to add one more that's slightly cleaner:

v2 = v1 ?? default(int);

Any Nullable<T> is implicitly convertible to its T, PROVIDED that the entire expression being evaluated can never result in a null assignment to a ValueType. So, the null-coalescing operator ?? is just syntax sugar for the ternary operator:

v2 = v1 == null ? default(int) : v1.Value;

...which is in turn syntax sugar for an if/else:

if(v1==null)
   v2 = default(int);
else
   v2 = v1.Value;

Also, as of .NET 4.0, Nullable<T> has a "GetValueOrDefault()" method, which is a null-safe getter that basically performs the null-coalescing shown above, so this works too:

v2 = v1.GetValueOrDefault();

Original Answer

In .NET it's rather ugly (until 4 or above):

StatusEnum MyStatus = (StatusEnum) Enum.Parse(typeof(StatusEnum), "Active", true);

I tend to simplify this with:

public static T ParseEnum<T>(string value)
{
    return (T) Enum.Parse(typeof(T), value, true);
}

Then I can do:

StatusEnum MyStatus = EnumUtil.ParseEnum<StatusEnum>("Active");

One option suggested in the comments is to add an extension, which is simple enough:

public static T ToEnum<T>(this string value)
{
    return (T) Enum.Parse(typeof(T), value, true);
}

StatusEnum MyStatus = "Active".ToEnum<StatusEnum>();

Finally, you may want to have a default enum to use if the string cannot be parsed:

public static T ToEnum<T>(this string value, T defaultValue) 
{
    if (string.IsNullOrEmpty(value))
    {
        return defaultValue;
    }

    T result;
    return Enum.TryParse<T>(value, true, out result) ? result : defaultValue;
}

Which makes this the call:

StatusEnum MyStatus = "Active".ToEnum(StatusEnum.None);

However, I would be careful adding an extension method like this to string as (without namespace control) it will appear on all instances of string whether they hold an enum or not (so 1234.ToString().ToEnum(StatusEnum.None) would be valid but nonsensical) . It's often be best to avoid cluttering Microsoft's core classes with extra methods that only apply in very specific contexts unless your entire development team has a very good understanding of what those extensions do.

C# – How to cast int to enum

From an int:

YourEnum foo = (YourEnum)yourInt;

From a string:

YourEnum foo = (YourEnum) Enum.Parse(typeof(YourEnum), yourString);

// The foo.ToString().Contains(",") check is necessary for enumerations marked with an [Flags] attribute
if (!Enum.IsDefined(typeof(YourEnum), foo) && !foo.ToString().Contains(","))
{
    throw new InvalidOperationException($"{yourString} is not an underlying value of the YourEnum enumeration.")
}

Update:

From number you can also

YourEnum foo = (YourEnum)Enum.ToObject(typeof(YourEnum) , yourInt);

Best Answer

Related Solutions

C# – Convert a string to an enum in C#

Original Answer

C# – How to cast int to enum

Related Topic