I have a property that returns System.Numerics.BigInteger. When I tried casting the property to an int, I got this error:
Cannot convert type 'System.Numerics.BigInteger' to 'int'
How can I convert ints to and from System.Numerics.BigInteger in C#?
The conversion from BigInteger to Int32 is explicit, so just assigning a BigInteger variable/property to an int variable doesn't work:
BigInteger big = ...
int result = big; // compiler error:
// "Cannot implicitly convert type
// 'System.Numerics.BigInteger' to 'int'.
// An explicit conversion exists (are you
// missing a cast?)"
This works (although it might throw an exception at runtime if the value is too large to fit in the int variable):
BigInteger big = ...
int result = (int)big; // works
Note that, if the BigInteger value is boxed in an object, you cannot unbox it and convert it to int at the same time:
BigInteger original = ...;
object obj = original; // box value
int result = (int)obj; // runtime error
// "Specified cast is not valid."
This works:
BigInteger original = ...;
object obj = original; // box value
BigInteger big = (BigInteger)obj; // unbox value
int result = (int)big; // works
BigInteger as int throws InvalidCastException with the message “Specified cast is not valid.” Which, again, isn't the error OP reported.Here are some choices that will convert BigInteger to int
BigInteger bi = someBigInteger;
int i = (int)bi;
int y = Int32.Parse(bi.ToString());
Watch Out though if the BigInteger value is too large it will throw a new exception so maybe do
int x;
bool result = int.TryParse(bi.ToString(), out x);
Or
try
{
int z = (int)bi;
}
catch (OverflowException ex)
{
Console.WriteLine(ex);
}
Or
int t = 0;
if (bi > int.MaxValue || bi < int.MinValue)
{
Console.WriteLine("Oh Noes are ahead");
}
else
{
t = (int)bi;
}
Having the int.Parse method only works if the initial BigInteger value would fit anyway. If not, try this:
int result = (int)(big & 0xFFFFFFFF);
Ugly? Yes. Works for any BigInteger value? Yes, as it throws away the upper bits of whatever is there.
BigInteger big = 3_000_000_000u; (int)(big & 0xFFFFFFFF) fails because 3_000_000_000u fits in uint and is less than 0xFFFFFFFF but overflows int. One correct way to truncate to int is unchecked((int)(uint)(big & uint.MaxValue)).By trying to improve the @lee-turpin answer when casting negative numbers, I came with a similar solution, but in this case without the issue with negative numbers. In my case, I was trying to have a 32-bit hash value from a BigInteger object.
var h = (int)(bigInteger % int.MaxValue);
Still ugly, but it works with any BigInteger value. Hope it helps.
int?int, so(int)someBigIntegershould work.