What do the logical functions IMP and EQV do in VB6? Has anyone found a real world use for them?

StackOverflow https://stackoverflow.com/questions/927119

  •  06-09-2019
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Question

And, Or, Xor and Not I understand. What I don't get are Imp and Eqv. What do they mean? How'd they get in there? Is there any real use for them?

Was it helpful?

Solution

IMP is "material implication" "a implies b" or "if a then b", which is equivalent to NOT a OR b. EQV is "equivalence" or "if and only if", so a EQV b is the same as (a IMP b) AND (b IMP a).

They got there because someone wanted to be complete. They can shorten some logical expressions, but you can always express the same thing with NOT and AND, NOT and OR, or with XOR alone.

OTHER TIPS

Here is the truth table for all the operators, both for boolean and for bitwise. The best time to use them is when you map your logic and realize you have a function that takes two inputs, and has the same outputs as those operators:)

------------------------------------------------------------------------------------------------------------------
|AND  |     |     |     |OR   |     |     |     |XOR  |     |     |     |IMP  |     |     |     |EQV  |     |     |
------------------------------------------------------------------------------------------------------------------
|In1  |In2  |Out1 |     |In1  |In2  |Out1 |     |In1  |In2  |Out1 |     |In1  |In2  |Out1 |     |In1  |In2  |Out1 |
------------------------------------------------------------------------------------------------------------------
|False|False|False|     |False|False|False|     |False|False|False|     |False|False|True |     |False|False|True |
------------------------------------------------------------------------------------------------------------------
|False|True |False|     |False|True |True |     |False|True |True |     |False|True |True |     |False|True |False|
------------------------------------------------------------------------------------------------------------------
|False|Null |False|     |False|Null |Null |     |False|Null |Null |     |False|Null |True |     |False|Null |Null |
------------------------------------------------------------------------------------------------------------------
|True |False|False|     |True |False|True |     |True |False|True |     |True |False|False|     |True |False|False|
------------------------------------------------------------------------------------------------------------------
|True |True |True |     |True |True |True |     |True |True |False|     |True |True |True |     |True |True |True |
------------------------------------------------------------------------------------------------------------------
|True |Null |Null |     |True |Null |True |     |True |Null |Null |     |True |Null |Null |     |True |Null |Null |
------------------------------------------------------------------------------------------------------------------
|Null |False|False|     |Null |False|Null |     |Null |False|Null |     |Null |False|Null |     |Null |False|Null |
------------------------------------------------------------------------------------------------------------------
|Null |True |Null |     |Null |True |True |     |Null |True |Null |     |Null |True |True |     |Null |True |Null |
------------------------------------------------------------------------------------------------------------------
|Null |Null |Null |     |Null |Null |Null |     |Null |Null |Null |     |Null |Null |Null |     |Null |Null |Null |
------------------------------------------------------------------------------------------------------------------
|     |     |     |     |     |     |     |     |     |     |     |     |     |     |     |     |     |     |     |
------------------------------------------------------------------------------------------------------------------
|In1  |In2  |Out1 |     |In1  |In2  |Out1 |     |In1  |In2  |Out1 |     |In1  |In2  |Out1 |     |In1  |In2  |Out1 |
------------------------------------------------------------------------------------------------------------------
|001  |001  |001  |     |001  |001  |001  |     |001  |001  |000  |     |001  |001  |111  |     |001  |001  |111  |
------------------------------------------------------------------------------------------------------------------
|001  |010  |000  |     |001  |010  |011  |     |001  |010  |011  |     |001  |010  |110  |     |001  |010  |100  |
------------------------------------------------------------------------------------------------------------------
|001  |011  |001  |     |001  |011  |011  |     |001  |011  |010  |     |001  |011  |111  |     |001  |011  |101  |
------------------------------------------------------------------------------------------------------------------
|001  |100  |000  |     |001  |100  |101  |     |001  |100  |101  |     |001  |100  |110  |     |001  |100  |010  |
------------------------------------------------------------------------------------------------------------------
|010  |001  |000  |     |010  |001  |011  |     |010  |001  |011  |     |010  |001  |101  |     |010  |001  |100  |
------------------------------------------------------------------------------------------------------------------
|010  |010  |010  |     |010  |010  |010  |     |010  |010  |000  |     |010  |010  |111  |     |010  |010  |111  |
------------------------------------------------------------------------------------------------------------------
|010  |011  |010  |     |010  |011  |011  |     |010  |011  |001  |     |010  |011  |111  |     |010  |011  |110  |
------------------------------------------------------------------------------------------------------------------
|010  |100  |000  |     |010  |100  |110  |     |010  |100  |110  |     |010  |100  |101  |     |010  |100  |001  |
------------------------------------------------------------------------------------------------------------------
|011  |001  |001  |     |011  |001  |011  |     |011  |001  |010  |     |011  |001  |101  |     |011  |001  |101  |
------------------------------------------------------------------------------------------------------------------
|011  |010  |010  |     |011  |010  |011  |     |011  |010  |001  |     |011  |010  |110  |     |011  |010  |110  |
------------------------------------------------------------------------------------------------------------------
|011  |011  |011  |     |011  |011  |011  |     |011  |011  |000  |     |011  |011  |111  |     |011  |011  |111  |
------------------------------------------------------------------------------------------------------------------
|011  |100  |000  |     |011  |100  |111  |     |011  |100  |111  |     |011  |100  |100  |     |011  |100  |000  |
------------------------------------------------------------------------------------------------------------------

IIRC, they both perform a bitwise !XOR on the two inputs and return the result.

They are not present in any of the .Net code base (unless you count the VB6 compatibility layer library) so should be considered deprecated and therefor ignored.

Off the top of my head I can't say as I've ever used them.

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