U3 LJ_ioGet_DIGITAL_BIT_STATE syntax

The information you are looking for is at the beginning of this page:

https://labjack.com/support/datasheets/u3/high-level-driver/example-pseu...

The listing of ioTypes notes which ones also set direction, so you don't want to use those.  The paragraph right after that listing talks more about this topic.  Here it is:

The general bit and port IOTypes automatically control direction, but the _DIR and _STATE ones do not. These can be used to read the current condition of digital I/O without changing the current condition. Note that the _STATE reads are actually doing a read using the input circuitry, not reading the state value last written. When you use LJ_ioGET_DIGITAL_BIT_STATE or LJ_ioGET_DIGITAL_PORT_STATE on a line set to output, it leaves it set as output, but it is doing an actual state read based on the voltage(s) on the pin(s). So if you set a line to output-high, but then something external is driving it low, it might read low.

Yes, the paragraph I quoted is pointing out that the _STATE registers do not change direction.  As for syntax, that is a general UD topic.  Syntax is usually not specific to the IOType, and indeed with LJ_ioGET_DIGITAL_BIT_STATE it has normal syntax.  Here is what I would say for syntax, and we will add this to the downloads page for each programming language:

The first step is to understand a general overview of the UD library:

https://labjack.com/support/datasheets/u3/high-level-driver/overview

The UD driver just has a handful of functions, and those all have the same 4-6 parameters.  Those parameters are described at the bottom of the Overview page.  Usually the meaning of each parameter should be apparent (e.g. Channel is the channel number you are operating on), but when it is not the pseudocode section should have any extra information that is needed.

Handle:  Always the handle.
IOType:  Always the IOType.
Channel:  If something besides a channel number the pseudocode section will tell you.
Value:  Always the value.
X1:  Usually not used, but if used the pseudocode section will tell you.
UserData:  Usually not used, but if used the pseudocode section will tell you.
 

So next you go to the pseudocode section:

https://labjack.com/support/datasheets/u3/high-level-driver/example-pseudocode/dio

The IOType LJ_ioGET_DIGITAL_BIT_STATE is listed at the beginning, and does not have any special comments.  The fact that it does not have any special comments tells you:

Channel is the channel you want to read.
Value is the value you will read.
X1 is not used.
UserData is not used.
 

There is certainly room for improvement.  I'd say there is 1 key reminder/hint that could be in more places.  Maybe the following key hint should be on every pseudocode page, along with a link that points you to the info I posted last time if someone is not sure about syntax.

    X1 & UserData:  If used for a particular IOType, the pseudocode section will tell you.
 

I would add that LJM (for the T4 and T7) is our 3rd generation library with 3rd generation documentation, so is improved in our opinion.  UD is not as active as LJM, but is still active so we do continue to make improvements to documentation.

Sometimes casting can be tricky with the x1 parameter because it is used in different ways.  I'll mark this for someone else to follow up, but I do see that the U3simple.cpp example in the VC6_LJUD archive uses some IOTypes that use x1.

https://labjack.com/support/software/examples/ud/vc6

GetFirstResult/GetNextResult are documented here:

https://labjack.com/support/software/api/ud/function-reference/getfirst-and-getnext

The px1 parameter in those functions are a pointer (long *px1). Pass a long variable by reference when using DIGITAL IOTypes.

    long lngIOType = 0;
    long lngChannel = 0;   
    double dblValue = 0;
    long lngX1 = 0;
    double dblUserData = 0;
    GetFirstResult(lngHandle, &lngIOType, &lngChannel, &dblValue, &lngX1, &dblUserData);

Alternatively you can also pass 0 to that parameter if you want to ignore its result:

    GetFirstResult(lngHandle, &lngIOType, &lngChannel, &dblValue, 0, 0);