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Guest
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 Posted: Tue Aug 15, 2006 9:10 am Post subject: Help with undefined references |
 |
|
Hi,
I know it must be a simple mistake, but I'm just learning C++ and can't
figure out what's wrong. Any help will be vey much appreciated 
I got the following error messages when the following program is
compiled and linked. What could be wrong?
Thanks,
Andre
/tmp/ccX0Z0Il.o(.text+0x17d): In function `Singleton::Instance()':
: undefined reference to `Singleton::theSingleton'
/tmp/ccX0Z0Il.o(.text+0x1ca): In function `Singleton::Instance()':
: undefined reference to `Singleton::theSingleton'
/tmp/ccX0Z0Il.o(.text+0x1cf): In function `Singleton::Instance()':
: undefined reference to `Singleton::theSingleton'
collect2: ld returned 1 exit status
#include <iostream>
class Singleton
{
public:
static Singleton * Instance();
~Singleton();
private:
Singleton();
static Singleton * theSingleton;
};
Singleton::Singleton()
{
std::cout << "Singleton constructot\n";
}
Singleton::~Singleton()
{
std::cout << "Singleton destructor\n";
}
Singleton * Singleton::Instance()
{
if( !theSingleton )
{
theSingleton = new Singleton();
}
return( theSingleton );
}
Singleton * theSingleton = 0;
int main()
{
return( 0 );
} |
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Isold.Wang@gmail.com
Guest
|
| Posted: Tue Aug 15, 2006 9:10 am Post subject: Re: Help with undefined references |
|
|
You can see this book <<Modern C++ Design>>
Chapter 6. Implementing Singletons
sieg1974 (AT) yahoo (DOT) com wrote:
| Quote: | Hi,
I know it must be a simple mistake, but I'm just learning C++ and can't
figure out what's wrong. Any help will be vey much appreciated
I got the following error messages when the following program is
compiled and linked. What could be wrong?
Thanks,
Andre
/tmp/ccX0Z0Il.o(.text+0x17d): In function `Singleton::Instance()':
: undefined reference to `Singleton::theSingleton'
/tmp/ccX0Z0Il.o(.text+0x1ca): In function `Singleton::Instance()':
: undefined reference to `Singleton::theSingleton'
/tmp/ccX0Z0Il.o(.text+0x1cf): In function `Singleton::Instance()':
: undefined reference to `Singleton::theSingleton'
collect2: ld returned 1 exit status
#include <iostream
class Singleton
{
public:
static Singleton * Instance();
~Singleton();
private:
Singleton();
static Singleton * theSingleton;
};
Singleton::Singleton()
{
std::cout << "Singleton constructot\n";
}
Singleton::~Singleton()
{
std::cout << "Singleton destructor\n";
}
Singleton * Singleton::Instance()
{
if( !theSingleton )
{
theSingleton = new Singleton();
}
return( theSingleton );
}
Singleton * theSingleton = 0;
int main()
{
return( 0 );
} |
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Greg
Guest
|
| Posted: Tue Aug 15, 2006 9:10 am Post subject: Re: Help with undefined references |
|
|
sieg1974 (AT) yahoo (DOT) com wrote:
| Quote: | Hi,
I know it must be a simple mistake, but I'm just learning C++ and can't
figure out what's wrong. Any help will be vey much appreciated
I got the following error messages when the following program is
compiled and linked. What could be wrong?
Thanks,
Andre
/tmp/ccX0Z0Il.o(.text+0x17d): In function `Singleton::Instance()':
: undefined reference to `Singleton::theSingleton'
/tmp/ccX0Z0Il.o(.text+0x1ca): In function `Singleton::Instance()':
: undefined reference to `Singleton::theSingleton'
/tmp/ccX0Z0Il.o(.text+0x1cf): In function `Singleton::Instance()':
: undefined reference to `Singleton::theSingleton'
collect2: ld returned 1 exit status
#include <iostream
class Singleton
{
public:
static Singleton * Instance();
~Singleton();
private:
Singleton();
static Singleton * theSingleton;
};
Singleton * theSingleton = 0;
|
Should be:
Singleton * Singleton::theSingleton = 0;
The member name needs to be qualified with its class name:
Greg |
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Salt_Peter
Guest
|
| Posted: Wed Aug 16, 2006 9:10 am Post subject: Re: Help with undefined references |
|
|
sieg1974 (AT) yahoo (DOT) com wrote:
| Quote: | Thanks for the help, I could make it work now. But I have another
question .
I have the following 2 versions of my program. The first one works
fine, but not the second one. I get the same linking erros as before.
Can anyone point out what could be wrong?
Thanks,
Andre
***********
Version 1
***********
#include <iostream
class Singleton
{
public:
static Singleton * Instance()
{
if( !theSingleton )
{
theSingleton = new Singleton();
|
try:
theSingleton = new Singleton;
| Quote: | }
return( theSingleton );
|
return theSingleton;
| Quote: | }
private:
static Singleton * theSingleton;
};
Singleton * Singleton::theSingleton = 0;
int main()
{
return( 0 );
}
***********
Version 2
***********
#include <iostream
class Singleton
{
public:
static Singleton * Instance();
private:
static Singleton * theSingleton;
};
Singleton * Singleton::Instance()
{
if( !theSingleton )
{
theSingleton = new Singleton();
|
same changes...
theSingleton = new Singleton;
| Quote: | }
return( theSingleton );
}
Singleton * Singleton::theSingleton = 0;
int main()
{
return( 0 );
|
return 0;
> } |
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