Declaring DoubleSolonoid

[RobHammann]

I have been trying to get solenoids to work all day, everything I try kicks back an error

grabSolenoid = new DoubleSolenoid(1, 1, 1);

always says "grabSolenoid is not a class"

What is the proper way to declare and run double solenoids? The screensteps isn't helping.

[Jon Stratis]

Try:

DoubleSolenoid grabSolenoid = new DoubleSolenoid(1, 1, 1);

[RobHammann]

Try:

DoubleSolenoid grabSolenoid = new DoubleSolenoid(1, 1, 1);

Could not convert '(operator new(104u), (<statement>, ((DoubleSolenoid*) <anonymous>)))' from' 'DoubleSolenoid*' to 'DoubleSolenoid'

[GeeTwo]

Oh, yeah, C++ forum...try:

DoubleSolenoid *grabSolenoid = new DoubleSolenoid(1, 1, 1);

[Jon Stratis]

Oops, my bad... The syntax is almost identical between java and c++, expert for that annoying *. I really hate dealing with punters in c++!

They issue you were having was that you hadn't declared your variable before assuming it, so the compiler didn't know what "grabSolenoid" was. By adding the class in front, you're telling the compiler what that is.

[one_each]

Here is a bit of explenation.

Could not convert '(operator new(104u), (<statement>, ((DoubleSolenoid*) <anonymous>)))' from' 'DoubleSolenoid*' to 'DoubleSolenoid'

The bolded parts are the important notes. Note the asterisk (or 'star') in the from and also note that it is missing in the to.

The new operator creates a new version of the class (DoubleSolenoid here) and returns a pointer to it. The asterisk (or 'star') indicates changes the type of grabSolenoid to a "pointer to DoubleSolenoid", thus making the types on both sides the same.

Pointers are one of the more confusing aspects of C/C++, however they are used everywhere. Remember, the pointer doesn't hold the data, it just points to where it is at. For classes, use the -> operator to access methods and fields from the pointer.

[RobHammann]

Thanks, they do declare now, however...


For classes, use the -> operator to access methods and fields from the pointer.


I really don't understand these pointers, when I try to set the solenoids using something like

grabSolenoid.set(DoubleSolenoid::kForward);

it says "request for member 'set' in '(((Robot*)this))->Robot::grabSolenoid', which is of pointer type 'DoubleSolenoid' (maybe you meant to use '->' ?)"

where do I put the ->?

[Steve Warner]

Try grabSolenoid->Set(DoubleSolenoid::kForward);

[Alan Anderson]

...using something like

grabSolenoid.set(DoubleSolenoid::kForward);

it says "request for member 'set' in '(((Robot*)this))->Robot::grabSolenoid', which is of pointer type 'DoubleSolenoid' (maybe you meant to use '->' ?)"

where do I put the ->?

You have declared grabSolenoid as a pointer to a double solenoid object. The member functions like Set() only work on an actual object. You need to dereference the pointer before you can call the function. The '->' is a small bit of syntax convenience that lets you dereference the pointer and do the equivalent of a '.' at the same time.

Just replace the '.' with '->' between the variable name and the function name.

[GeeTwo]

Just replace the '.' with '->' between the variable name and the function name.

Yes. obj_ptr->elt is equivalent to (*obj_ptr).elt . That is, look up the actual field or method within the object that obj_ptr points to.

[Joe Ross]

grabSolenoid = new DoubleSolenoid(1, 1, 1);

Once you get the syntax correct, you'll want to make sure you're allocating unique channels, as you'll likely get a runtime error as written.

[RobHammann]

Well it seems to have worked, I cant test it yet on actual solenoids, but it builds and deploys just fine