C# performing bitwise operation with & from C++

Question

Anyway here's my problem I have been modifying a whole C++ program to work in C# and I am pretty much done, I have this If statement in the C++ program.

if(info[i].location & 0x8 || 
             info[i].location & 0x100|| 
                     info[i].location & 0x200)
{
    //do work
}
else
{
    return
}

And of course when I do this in C# it gives me a "Operator '||' cannot be applied to operands of type 'int' and 'int'" error.

Any clue on what my problem is, Im guessing that C# has got a way of doing this as I am fairly unfamiliar with these old C operators.

Jon Skeet · Accepted Answer · 2012-08-02 21:09:54Z

10

Why it fails

Fundamentally it's the same difference as this:

if (someInteger) // C or C++

vs

if (someInteger != 0) // C#

Basically C# is a lot stricter when it comes to logical operators and conditions - it forces you to have use something which is either bool or convertible to bool.

As an aside, that's also why in C# this isn't just a warning, but a full-blown error:

int x = ...;
if (x = 10) // Whoops - meant to be == but it's actually an assignment

If you see comparisons this way round:

if (10 == x)

That's usually developers trying to avoid typos like the above - but it's not needed in C# unless you're really comparing against constant bool values.

Fixing the problem

I suspect you just need:

if (((info[i].location & 0x8) != 0)) ||
    ((info[i].location & 0x100) != 0)) ||
    ((info[i].location & 0x200) != 0)))

It's possible that you don't need all of those brackets... but another alternative is just to use one test:

if ((info[i].location & 0x308) != 0)

After all, you're just testing whether any of those three bits are set...

You should also consider using a flags-based enum:

[Flags]
public enum LocationTypes
{
    Foo = 1 << 3; // The original 0x8
    Bar = 1 << 8; // The original 0x100
    Baz = 1 << 9; // The original 0x200
}

Then you could use:

LocationTypes mask = LocationTypes.Foo | LocationTypes.Bar | LocationTypes.Baz;
if ((info[i].location) & mask != 0)

Or using Unconstrained Melody:

LocationTypes mask = LocationTypes.Foo | LocationTypes.Bar | LocationTypes.Baz;
if (info[i].location.HasAny(mask))

edited Aug 2, 2012 at 21:09

answered Aug 2, 2012 at 21:04

Jon Skeet

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2 Comments

Doug T. Over a year ago

Or even better--define each bit as a constant and bitwise-or them together into a mask to compare against

Jon Skeet Over a year ago

@DougT.: That's pretty much what my last edit was about - but instead of several integer constants, use an enum.

ikh · Accepted Answer · 2012-08-02 21:10:52Z

4

It's pretty much exactly what it says: in C#, || is a logical-only operator and so cannot work on int. You can replace || with | (the bitwise-or which works on ints), but then the entire expression will need to be converted to boolean by comparing it to zero, because in C# the if-statements require a boolean.

Alternatively, you can replace info[i].location & 0x8 with (info[i].location & 0x8 != 0).

edited Aug 2, 2012 at 21:10

answered Aug 2, 2012 at 21:04

ikh

2,4362 gold badges21 silver badges30 bronze badges

2 Comments

Marlon Over a year ago

+1, better answer because it explains why the compiler is giving an error.

Scott Selby Over a year ago

Jon Skeet was just way faster

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