Handling integer overflow is a common task, but what's the best way to handle it in C#? Is there some syntactic sugar to make it simpler than with other languages? Or is this really the best way?
int x = foo();
int test = x * common;
if(test / common != x)
Console.WriteLine("oh noes!");
else
Console.WriteLine("safe!");
I haven't needed to use this often, but you can use the checked keyword:
int x = foo();
int test = checked(x * common);
Will result in a runtime exception if overflows. From MSDN:
In a checked context, if an expression produces a value that is outside the range of the destination type, the result depends on whether the expression is constant or non-constant. Constant expressions cause compile time errors, while non-constant expressions are evaluated at run time and raise exceptions.
I should also point out that there is another C# keyword, unchecked, which of course does the opposite of checked and ignores overflows. You might wonder when you'd ever use unchecked since it appears to be the default behavior. Well, there is a C# compiler option that defines how expressions outside of checked and unchecked are handled: /checked. You can set it under the advanced build settings of your project.
If you have a lot of expressions that need to be checked, the simplest thing to do would actually be to set the /checked build option. Then any expression that overflows, unless wrapped in unchecked, would result in a runtime exception.
Try the following
int x = foo();
try {
int test = checked (x * common);
Console.WriteLine("safe!");
} catch (OverflowException) {
Console.WriteLine("oh noes!");
}
The best way is as Micheal Said - use Checked keyword. This can be done as :
int x = int.MaxValue;
try
{
checked
{
int test = x * 2;
Console.WriteLine("No Overflow!");
}
}
catch (OverflowException ex)
{
Console.WriteLine("Overflow Exception caught as: " + ex.ToString());
}
Sometimes, the simplest way is the best way. I can't think a better way to write what you wrote, but you can short it to:
int x = foo();
if ((x * common) / common != x)
Console.WriteLine("oh noes!");
else
Console.WriteLine("safe!");
Note that I didn't remove the x variable because it'd be foolish to call the foo() three times.
Old thread, but I just ran into this. I didn't want to use exceptions. What I ended up with was:
long a = (long)b * (long)c;
if(a>int.MaxValue || a<int.MinValue)
do whatever you want with the overflow
return((int)a);
int.MaxValue + 1 gives you -2147483648 or int.MinValue. so a can never be larger than MaxValue or smaller than MinValue. Think of numbers as a line like this: -2147483648, -2147483647, ... 0 ... 2147483646, 2147483647 when you go over the max value, it flows back to the smallest.
So, I ran into this far after the fact, and it mostly answered my question, but for my particular case (in the event anyone else has the same requirements), I wanted anything that would overflow the positive value of a signed int to just settle at int.MaxValue:
int x = int.MaxValue - 3;
int someval = foo();
try
{
x += someval;
}
catch (OverflowException)
{
x = int.MaxValue;
}
/checked, or use the checked keyword, correct?