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New Class made -> error LNK2019: unresolved external symbol

Started by Programming020195BRook Dec 10, 2012 at 2:28 AM 9 replies 6.9k views

Original Post

Programming020195BRook

Dec 10, 2012 at 2:28 AM

I'm getting the error:

1>main.obj : error LNK2019: unresolved external symbol "class City __cdecl Ice_Palace_City(void)" (?Ice_Palace_City@@YA?AVCity@@XZ) referenced in function _main

I cannot figure out why this is occurring.... I made the City.h file and setup all my prototypes, then made the City.cpp file to declare everything, now when I use the class I get this error.

Any reason why this is happening?

I have #include "City.h" in my main.cpp file, and City.cpp file.

What can I do to fix this? Only thing that changed since my last successful build was adding this class.

wqking

Dec 10, 2012 at 3:16 AM

Please show your code, especially the error related function/class.

Programming020195BRook

Dec 10, 2012 at 3:27 AM

EDIT: Never mind, I see the problem, I shouldn't have initialized it as City Ice_Palace_City() -> But Ice_Palace_City.

Stupid mistake!

wqking

Dec 10, 2012 at 3:29 AM

The unresolved symbol is Ice_Palace_City, so please show the declaration and definition of function Ice_Palace_City...

wqking

Dec 10, 2012 at 3:40 AM

EDIT: Never mind, I see the problem, I shouldn't have initialized it as City Ice_Palace_City() -> But Ice_Palace_City.

Stupid mistake!

Not that stupid.
That's another C++ quirk.
When defining an object value, if using default constructor, we can't write the "()" because it will be treated as function declaration, but if not the default constructor, we have to give "()".
MyClass obj; // can't have ()
MyClass obj(1, "abc");

Programming020195BRook

Dec 10, 2012 at 3:42 AM

Thanks! It is a stupid mistake for me because I made hundreds of classes, but somehow I missed this... I guess the 3 week break from programming didn't do me any good! Almost as bad as when I left only one "=" in an if statement, and couldn't find out why a function was acting up.

Oh well... Thanks!

bluepig.man

Dec 10, 2012 at 11:42 AM

Oh?l thank it's a strange mistake.it;s always meet by chance.

Aardvajk

Dec 10, 2012 at 2:39 PM

This can crop up in all sorts of weird and unexpected ways:

[source]
class Point
{
public:
Point(float x, float y){ }
};

void f()
{
int x = 10, y = 16;

Point p(float(x), float(y)); // blurgh
}
[/source]

That case had me scratching my head for a long time the first time I encountered it. I believe the rule is that if the compiler is able to treat it as either a declaration or a function prototype, it is required to favour the prototype interpretation of the token list.

As an aside, this particular case is another seldom quoted reason to prefer static_cast<> style casts.

wqking

Dec 10, 2012 at 3:02 PM

That case had me scratching my head for a long time the first time I encountered it. I believe the rule is that if the compiler is able to treat it as either a declaration or a function prototype, it is required to favour the prototype interpretation of the token list.

As an aside, this particular case is another seldom quoted reason to prefer static_cast<> style casts.

+1
Very interesting example, I didn not know it before.
But is that standard c++ to treat point p(float(x), float(y)) as function declaration?

Brother Bob

Dec 10, 2012 at 3:43 PM

But is that standard c++ to treat point p(float(x), float(y)) as function declaration?

It is, unfortunately.

SiCrane

Dec 10, 2012 at 3:47 PM

The relevant part of the standard is section 6.8 in all of C++98, 03 and 11. For more information you can look up most vexing parse.

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