Better method for converting int to short? (NULL if not possible)

Question

I have following two approaches for converting int to short?.

1. First one fails if the value is not in short range.
2. The second approach works but it has a unnecessary conversion to string.

Is there a better method?

EDIT:

From the answer below:

Int16 is just a subset of Int32 so you do not need any conversion to "intermediate" types.

CODE

//Approach 1
int vIn = 123456789;
short? vOut = Convert.ToInt16(vIn);
//Value was either too large or too small for an Int16.

//Approach 2
short? vOut2 = null;
int vIn2 = 123456789;
short number;
string characterRepresentationOfInt = vIn2.ToString();
bool result = Int16.TryParse(characterRepresentationOfInt, out number);
if (result)
{
    vOut2 = number;
}

Reference:

1. Java: Conversion from int to short

Answer 1

Why you can't simply use the built-in conversion of the cast? Just add a check to be sure it's not out of range (if you want a null value instead of an exception).

short? ConvertToShort(int value)
{
    if (value < Int16.MinValue || value > Int16.MaxValue)
        return null;

    return (short)value;
}

About your approaches:

1. It works (of course) but you'll never get the null value and conversion may fail if value is outside the valid range of Int16.

2. It's terribly slow. Don't forget Int16 is just a subset of Int32 so you do not need any conversion to "intermediate" types.

Answer 2

Here are a couple of possible solutions.

Static helper method:

public static class Number
{
    public static bool TryConvertToShort(int value, out short result)
    {
        bool retval = false;
        result = 0;
        if (value > Int16.MinValue && value < Int16.MaxValue)
        {
            result = Convert.ToInt16(value);
            retval = true;
        }

        return retval;
    }
}

Usage:

int a = 1234;
short b;
bool success = Number.TryConvertToShort(a, out b);

Extension method:

public static class ExtendInt32
{
    public static bool TryConvertToShort(this int value, out short result)
    {
        bool retval = false;
        result = 0;
        if (value > Int16.MinValue && value < Int16.MaxValue)
        {
            result = Convert.ToInt16(value);
            retval = true;
        }

        return retval;
    }
}

Usage:

int a = 1234;
short b;
bool success = a.TryConvertToShort(out b);

You can also create a helper/extension method that doesn't fail gracefully and instead either returns a default value (0) or throws an exception.

public static short ConvertToShort(int value)
{
    short result;
    if (value > Int16.MinValue && value < Int16.MaxValue)
    {
        result = Convert.ToInt16(value);
    }
    else
    {
        throw new OverflowException();
    }

    return result;
}