Undefined reference to 'fabs' on arduino ide 1.8 about tinyexpr HOT 10 CLOSED

What is the commandline you're using to compile?

Maybe you need something like the -lm flag to link in the math library?

I really don't know. You might have better luck posting in an Arduino forum. Please report back if you do figure it out, though.

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I am not using command line to compile. I think the arduino ide automates the process. I will try to get help with the arduino forum. But likely they will respond to contact the author to fix the issue though.

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You should be able to see what the IDE is passing to the compiler somehow. I think it could be very helpful to know.

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I assume you've also added tinyexpr.c into your project somehow. You may need to make sure that it is being compiled as C and not as C++. Just a thought.

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Yes, I setup the ide to include your library including the source and the header file. It don't complain about undefined reference to the first function in the library which is te_interp so the library is included in the right way. I think the error is somewhere in line 119 on tinyexpr.c.

static const te_variable functions[] = {
118	    /* must be in alphabetical order */
119	    {"abs", fabs,     TE_FUNCTION1 | TE_FLAG_PURE, 0},

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What happens if you comment out line 119? Does it then complain that acos (from line 120) is undefined?

It seems like it's not linking against the math library. The usual way to do that on gcc is with the -lm flag. It could also be a C to C++ name mangling issue.

It also may be that the Arduino doesn't support pointers to functions, in which case you'd be out of luck.

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I tried your suggestion. It compiles successfully after commenting the fabs line. Do you know what is happening?

Maybe it is arduino issue?

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No, that's really odd. fabs is very much part of standard C.

TinyExpr should work fine with that line commented out, you just won't have access to the abs function (you could write your own very easily though).

You should ask someone who knows about Arduino and report back.

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Ok. I will. Thanks for the heads up.

By the way, can you add bitwise operations like &, | and !?
Those operations are very important to embedded systems.

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TinyExpr works with floating point, so bitwise operators don't really make sense there.

You could probably fork TinyExpr to use integers (I know at least one person already has) and then add those operators yourself pretty easily.

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