Error: Unresolved external Symbol

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2.50/5 (2 votes)

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Hello there,

I'm working on a piece of code. I need to access a variable from one class which is declared in another one.

For Example:

C++

Class Sum
{
double time;
}

class Calc
{
static Sum ss; // reference to the Sum class
}

class Settings :: setup()
{
Calc:: ss.time 
}

I had to make sum static in order to aceess the variable but I get an error that says Unresolved external Symbol

public: static class Sum Geo::ss" (?ss@Geo.....bla bla)

Posted 27-Mar-12 1:52am

Sumal.V

Updated 27-Mar-12 2:31am

member60

v2

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CPallini · Accepted Answer · 2012-03-27T02:05:00

Solution 1

static variables must defined in a source file (you provided only the declaration). Put, for instance, in the class Calc source file (say "calc.cpp") the variable definition:

C++

Sum Calc::ss;

Posted 27-Mar-12 2:05am

CPallini

Comments

Sumal.V 27-Mar-12 8:21am

But when I try that and access the variable it still says non static member reference must be relative to a particualr object.

CPallini 27-Mar-12 8:32am

Please show your actual (current) code.

Sumal.V 27-Mar-12 8:40am

Well its a massive code, I will show u the main bits.

1) class AFX_EXT_EDATA Sum : public CMainSum
{
double time1;
double time2;
}

2)class AFX_EXT_EDATA Calc
{
Sum Calc :: ss;
}

3) void Settings::SetupCtrls()
{
InsCtrl(80, EC_EDIT, Calc::ss.time2); //I get the error here!
}

This error goes if I declare Sum in calc as static but again gives the unresolved external symbol error!!!

CPallini 27-Mar-12 8:52am

The following code works:

#include <iostream>

using namespace std;
class Sum
{
public:
double time1;
double time2;
Sum(){time1=0.5; time2=0.7;}
};

class Calc
{
public:
static Sum ss;
};

void SetupCtrls()
{
cout << Calc::ss.time2 << endl;
}

Sum Calc::ss; // STATIC VARIABLE DEFINITION

int main()
{
SetupCtrls();
}

Stefan_Lang 27-Mar-12 12:17pm

When you write Calc::, then the symbol after that can only be static: either a static member variable, or a type defined in that class, or a function name. static means that you can have as many objects of that class as you like, but you'll only have exactly one value of that static variable. In effect, static means global.

If you want to access a non-static member of a class, you need to have an instance of that class, and then access members of that instance using '.' or '->'. Example:

class Calc {
public:
   Sum ss;
};
int main() {
   Calc myCalcInstance1; // myCalcInstance1 is one instance of class Calc
   Calc myCalcInstance2; // this is another instance; now you have two instances
   myCalcInstance1.ss.time1 = 0.1; // access value in first instance
   myCalcInstance2.ss.time1 = 2.3; // access value in second instance
   return 0;
}

Sumal.V 27-Mar-12 9:02am

Sorry I didn't understand where u have declared "Sum Calc::ss".

Stefan_Lang 27-Mar-12 12:04pm

It's declared in class Calc, and defined right above the main() function.

Sumal.V 27-Mar-12 9:43am

When I declare Sum Calc::ss.time1, The error is where Sum is declared which says "Type name not allowed"

Stefan_Lang 27-Mar-12 12:06pm

Wrong syntax. The static variable declared in CPallini's code is Calc::ss, not Calc::ss.time1.

Sumal.V 28-Mar-12 11:06am

Oh well thank you.

I had only defined the variable in the .h class but not in the .cpp

My code works perfectly fine now.

Thanks for ur time. :)

CPallini 29-Mar-12 3:26am

You are welcome.