unchecked (C# Reference)
The unchecked keyword is used to suppress overflow-checking for integral-type arithmetic operations and conversions.
Remarks
In an unchecked context, if an expression produces a value that is outside the range of the destination type, the result is truncated. For example:
unchecked
{
int val = 2147483647 * 2;
}
Because the calculation above is performed in an unchecked block, the fact that the result is too large for an integer is ignored, and val is assigned the value -2. By default, overflow detection is enabled, which has the same effect as using checked.
In the example above, had unchecked been omitted, a compilation error would occur because the expression uses constants and the result is known at compile time. The unchecked keyword also suppresses overflow detection for non-constant expressions, which otherwise result in OverflowException at runtime.
The unchecked keyword can also be used as an operator, like this:
public int UncheckedAdd(int a, int b)
{
return unchecked(a + b);
}
Example
This sample shows how to use the unchecked statement, using unchecked with constant expressions.
// statements_unchecked.cs
using System;
class TestClass
{
const int x = 2147483647; // Max int
const int y = 2;
static void Main()
{
int z;
unchecked
{
z = x * y;
}
Console.WriteLine("Unchecked output value: {0}", z);
}
}
Output
Unchecked output value: -2
C# Language Specification
For more information, see the following sections in the C# Language Specification:
5.3.3.2 Block statements, checked, and unchecked statements
7.5.12 The checked and unchecked operators
8.11 The checked and unchecked statements
See Also
Reference
C# Keywords
Checked and Unchecked (C# Reference)
checked (C# Reference)