Multiple conditions in one case

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Hi! I need to use multiple conditions in one case.
This is my code:

C++

#define BLUE           0x00010000
#define GREEN          0x00000001
#define RED            0x00020000


DWORD Colors = BLUE | GREEN;

	switch(Colors)
	{
		case BLUE | RED, BLUE | GREEN:
		{
		OutputDebugString("OK");
		break;
		}
	}

If I set Colors to BLUE | GREEN the condition executes successfully and I can see "OK" message.

But if I set Colors to BLUE | RED - there are nothing happens.

It is important: do not move BLUE | RED and BLUE | GREEN to separate cases.

why is it not working? And is it possible to implement it?

Thanks!

Posted 20-Nov-15 11:27am

Igor-84

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Matt T Heffron · Accepted Answer · 2015-11-20T11:46:00

Solution 1

A case can contain only a single constant expression. The comma is not giving you two different cases that lead to the same code, it is evaluating both expressions and then throwing away the first one.
See: Comma Operator[^]
The case specifies a value which the expression in the switch must exactly match, there's no way to perform any analysis to the matching.
~~I think~~ I'm sure the only way to accomplish this is to violate the constraint on not separating them:

C++

switch(Colors)
{
    case BLUE | RED:
    case BLUE | GREEN:
    {
    OutputDebugString("OK");
    break;
    }
}

Posted 20-Nov-15 11:46am

Matt T Heffron

Updated 20-Nov-15 11:55am

v2

Comments

Igor-84 20-Nov-15 17:59pm

Explain me please, "not separating them" - is it violation?

Matt T Heffron 20-Nov-15 18:08pm

In your original question you specified:
It is important: do not move BLUE | RED and BLUE | GREEN to separate cases.
This is the "constraint" to which I was referring.
The only way to get the behavior you seem to be trying to accomplish is to use separate cases which would "violate" your "constraint".

Igor-84 20-Nov-15 18:16pm

Thanks!

User 59241 · Accepted Answer · 2015-11-20T11:46:00

Solution 2

Where did you find that syntax? It will always evaluate to the right most statement.
http://stackoverflow.com/questions/9358224/case-command-for-checking-two-values[^]

Do:

C++

DWORD Colors = BLUE | GREEN;
 
	switch(Colors)
	{
		case BLUE | RED:
               case BLUE | GREEN:
		{
		OutputDebugString("OK");
		break;
		}
	}

Posted 20-Nov-15 11:46am

User 59241

Updated 20-Nov-15 11:49am

v2

Comments

Igor-84 20-Nov-15 17:55pm

Thanks! I have translated a similar code from Delphi to C++. In Delphi it is permissible.