C++ pass enum to object constructor

Question

Say I have the following:

Foo::Foo() {
value = 25; //default constructor...
}

Foo::Foo(Enum bar) {
value = (int)bar; //purpose is to allow an integer to take enum constant's integer value.
}

from...

enum Enum 
{
A = 25,
B = 50,
}

class Foo 
{
public:
    Foo();
    Foo(Enum bar);
private:
int value;
}

Yet, if I do the following:

Enum bar = A; //A = 25

Foo * foo = new Foo(A); //error: "undefined reference to Foo::Foo(Enum)"

This is in Eclipse CDT 3.6. Why is this happening? Is there anything I can do about this to solve the problem?

you forgot to implement Foo::Foo(Enum); ? Say like the .cpp didn't get compiled properly? — tp1
– tp1, Commented Jul 21, 2011 at 3:37
@tp1 No, the .cpp is identical to the .h file in terms of method signatures. — zeboidlund
– zeboidlund, Commented Jul 21, 2011 at 4:09
in what file is Foo::Foo(Enum bar) implemented? Is that file included in the project file (i.e., is it actually being compiled)? — Cechner
– Cechner, Commented Jul 21, 2011 at 4:11

Darren Engwirda · Accepted Answer · 2011-07-21 03:39:38Z

4

After fixing a few syntax errors (extra , in Enum definition, missing ; after Enum and Foo definitions), your code was run-able in gcc. Check here: http://www.ideone.com/GZdNM

I don't really understand what you're trying to do with the enum, but for sure, calling it Enum is probably not a great idea...

answered Jul 21, 2011 at 3:39

Darren Engwirda

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1 Comment

zeboidlund Over a year ago

That was just an example name. The real Enum name is just "BoostAmount". The idea is to pass the enum value to the constructor, and an integer field takes on the integer value the enum represents. My header file is included via absolute path, so I'm not sure how it works for you but it doesn't for me. If there are any questions I can answer, I'd be happy to.

Mark B · Accepted Answer · 2011-07-21 04:20:04Z

1

It sounds like you forgot to link foo.C into your final application.

answered Jul 21, 2011 at 4:20

Mark B

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4 Comments

zeboidlund Over a year ago

Sorry, I'm not quite following. What do you mean, exactly?

Tony Delroy Over a year ago

+1. @Holland: If you put the implementation of Foo::Foo(Enum) in a separate file - say foo.c++, then the normal compiler behaviour if you compile that file is to produce foo.o. You then need to tell the compiler to link foo.o when compiling the file containing main(). On UNIX/Linux, you'd normally write a Makefile to do this, but I'm not sure what Eclipse expects.

zeboidlund Over a year ago

@Tony Thanks for your assistance, Tony. My Eclipse project is actually setup to use a Makefile to do the compiling. Is there any quick snippet I could write within the Makefile which you know of that could do this?

Tony Delroy Over a year ago

@Holland: at absolute simplest, you want app: <tab> app.c++ foo.o on one line, <tab> g++ -o app app.c++ foo.o on the next.

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