Unresolved externals with inline constructor

Question

I have a simple 2 dimensional vector class, which is implemented as inline functions/operators.

However when I want to instantiate my Vector with no parameters I get Unresolved externals error and I'm not sure why. However, when I use other constructor with parameters it's ok.

This is my class:

class Vector2
{
public:
   float x;
   float y;

public:
   //Constructors
   Vector2() : x(0.0f), y(0.0f) {}
   Vector2(const float _x, const float _y) : x(_x), y(_y) { }
};

Creating instance which causes error:

Vector2 a();

But when instantiating with other constructor it's ok. This also works:

Vector2 a = Vector2();

I'm getting this:

1>main.obj : error LNK2019: unresolved external symbol "class GreenEye::Maths::Vector2 __cdecl a(void)" (?a@@YA?AVVector2@Maths@GreenEye@@XZ) referenced in function main
1>X:\Development\Projects\Engine\x64\Debug\Test.exe : fatal error LNK1120: 1 unresolved external

Any ideas? Thanks.

Missing semi-colon `;` after final brace of class declaration. Other than that, I cannot reproduce your issue. — bku_drytt, Oct 06 '15 at 21:23
Edited, forgot to add it here in code, anyway that's not an issue — mezo, Oct 06 '15 at 21:26
Cannot reproduce when adding the missing semi-colon too, as with @bku_drytt. — AStopher, Oct 06 '15 at 21:28
N.B. Functions defined in the class body are implicitly inline, so saying `inline` on them is redundant. The semi-colons after the function bodies are redundant too. — Jonathan Wakely, Oct 06 '15 at 21:31
`Vector2 a();` is a declaration of a function named `a` that takes no arguments and returns a `Vector2` instance by value. Look up "most vexing parse". — Praetorian, Oct 06 '15 at 21:41
@Lightness [Maybe, maybe not](http://stackoverflow.com/questions/28598673/why-strange-behaviour-with-operator#comment45503661_28598673). — Praetorian, Oct 06 '15 at 22:33
@Praetorian: Nope, just the "not". Scott is wrong. TC (and me) are right. :) — Lightness Races in Orbit, Oct 06 '15 at 22:36

score 5 · Accepted Answer · answered Oct 06 '15 at 21:42

5

It's because you are not instantiating an object using the following:

Vector2 a();

This is actually a function declaration which is why it's complaining about the missing function at link time.

To create an object using the default constructor it should be:

 Vector2 a;

answered Oct 06 '15 at 21:42

Scott

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This problem is common enough to have a name: the most vexing parse. – Mark Ransom Oct 07 '15 at 03:28

Unresolved externals with inline constructor

1 Answers1