need help on compilation link error LNK2001

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Could anyone help me out to solve this linking error. Not sure why this happens:

Error   1   error LNK2001: unresolved external symbol "protected: virtual class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > __thiscall cPlainKey::Print(void)" (?Print@cPlainKey@@MAE?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@XZ)  data.obj

the code which is involved in this:

C++

#define cString std::string

class cPlainKeyDummy : public cPlainKey {
private:
  char *str;
protected:
  virtual cString Print(void);
}

cString cPlainKey::ToString(bool hide)
{
	char *tmp;
	sprintf(tmp, (hide ? "%c %.*X %s %.4s..." : "%c %.*X %s %s"),type,IdSize(),id,&PrintKeyNr(),&Print());
	return tmp;
}

cString cPlainKeyDummy::Print(void)
{
    return string(str);
}

Adding mising data:

C++

class cPlainKey : public cSimpleItem {
friend class cPlainKeys;
friend class cMutableKey;
private:
  bool au, del, super;
protected:
  virtual cString Print(void);//=0;

public:
  int type, id, keynr;

  };
class cMutableKey : public cPlainKey {
private:
  cPlainKey *real;
protected:
  virtual cString Print(void);
  virtual cPlainKey *Alloc(void) const=0;
public:
  };

class cSimpleListBase;

class cSimpleItem {
friend class cSimpleListBase;
private:
  cSimpleItem *next;
public:
  virtual ~cSimpleItem() {}
  cSimpleItem *Next(void) const { return next; }
  };


cString cMutableKey::Print(void)
{
  return real->Print();
}

cString cPlainKey::PrintKeyNr(void)
{
	char ret[16];
	sprintf(ret, "%02X",keynr);
  return string(ret);
}

int cPlainKey::IdSize(void)
{
  return id>0xFF ? (id>0xFFFF ? 6 : 4) : 2;
}

File is quite big, so I am trying to find all print()...
The code compiles fine it's just not linking.

Posted 12-Jan-12 3:44am

Tomazas77

Updated 12-Jan-12 5:30am

v5

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Comments

ErnestoNet 12-Jan-12 9:55am

If you read the linking error, the problem is
<PRE>
cPlainKey::Print(void)
</PRE>

You should post the definition of class cPlainKey to find the error.

6 solutions

Solution 1

The linker did not find the function cPlainKey::Print(). It's not present. Present is a function cPlainKeyDummy::Print() (note the 'Dummy').

If this is solved your code will crash. You are using an unitialized char pointer as argument to sprintf. The cPlainKey::str member is another possible candidate.

With warning level 4 you should see a lot of compiler warnings. You should set level 4 in the compiler options of your project. Then you will hopefully have a warning about the return values of your ToString() (cString defined, char* used) and Print() (cString defined, string used) functions.

Finally one question: Why did you use #define cString std::string?
It makes your code less readable.

Posted 12-Jan-12 4:21am

Jochen Arndt

Comments

Tomazas77 12-Jan-12 11:05am

I used #defined cString because this code copy and paste. More simple to define than to do replacement.

Setting warning to level 4 does not add more errors, just one.

Jochen Arndt 12-Jan-12 11:16am

Still the linker error? According to the updated question, you have a definition of the Print() member, but no implementation. And the cPlainKeyDummy::Print() implementation should generate the error ''cPlainKeyDummy': No class or namespace' if the class is not defined elsewhere.

Tomazas77 12-Jan-12 11:40am

yes, still have linker problem

Jochen Arndt 12-Jan-12 11:46am

And where is your implementation of cPlainKey::Print()?

Tomazas77 12-Jan-12 11:48am

just declaration virtual in class.

Jochen Arndt 12-Jan-12 11:51am

That is the error. You need an implementation.

Solution 2

I'm not sure how you get the Linker error since the above code will not compile. Where is the class definition of cPlainKey?

Posted 12-Jan-12 4:25am

Richard MacCutchan

Comments

Tomazas77 12-Jan-12 11:06am

just added to question

Solution 3

Jochen is correct, the linker is pointing to cPlainKey::Print() which we can't tell you if there's a problem with if (as Richard stated) you don't show us the definition of cPlainKey.

The other possible problem that may be causing this (if you DON'T have a cPlainKey::Print()) is that you have a pointer to a cPlayKeyDummy object that you're treating as a cPlainKey type and still trying to access cPlayKeyDummy::Print(). This would give you the same exact linker error.

Posted 12-Jan-12 4:52am

Albert Holguin

Solution 4

C++

#define cString std::string

As has been pointed out, this #define is questionable. And it's bad style for C++. If you really need an alias, use typedef instead.

C++

class cPlainKeyDummy : public cPlainKey {

At this point we must ask: where's the definition of cPlainKey?

C++

protected:
  virtual cString Print(void);

While this may not necessarily be the case, this implies there is a virtual function of that same name defined in the base class.

C++

If that's the closing bracket for your class definition, you're missing a ';' here!

C++

cString cPlainKey::ToString(bool hide)

Why did you post that code? I don't see it's being used in the rest of the code you posted. Has something gone missing you meant to post as well?

C++

char *tmp;
sprintf(tmp, (hide ? "%c %.*X %s %.4s..." : "%c %.*X %s %s"),type,IdSize(),id,&PrintKeyNr(),&Print());
return tmp;

Ugh, that is wrong on so many levels ...

* First, you define a char pointer and don't initialize it.
* Then you create a string using that pointer without allocating memory first - so you're writing into an undefined memory location!
* Next, the format string you use - both of them - refer to 4 values, but then you provide 5 parameters!?
* Looking at these parameters, the last two are addresses? You didn't provide the prototype for PrintKeyNr(), but the return type of Print() is of type std::string, and address-of(std::string) is not a valid argument type you can sensibly pass to sprintf, except for printing a memory address! Of course, this consideration is moot since that is the fifth parameter which will be ignored anyway...
* Besides, what are the symbols type, id, and the function IdSize()?
* P.S.: most of the format specifiers don't make much sense to me either, e. g. 's' denotes a string and '.NN' refers to decimals of a float - so what does '%.4s' mean?

C++

cString cPlainKeyDummy::Print(void)
{
    return string(str);
}

What exactly is the function string? and what is the symbol str referring to?

We may not need all the information I asked about, but you at least have to give us some, and then copy it correctly, so we can properly parse the relevant information. Most importantly, the linker complained about a missing function implementation: std::string cPlainKey::Print(void), and that means you called it somewhere: please show us the code where you create the cPlainKey object and call the function.

Posted 12-Jan-12 5:16am

Stefan_Lang

Updated 12-Jan-12 5:26am

v2

Comments

Jochen Arndt 12-Jan-12 11:24am

Regarding your last question: The Print() function is called from within ToString().

And thanks for checking all errors in that function. I stopped analyzing after recognition of the unitialized pointer.

Stefan_Lang 12-Jan-12 11:31am

The Print() function is called from within ToString().
Oh yeah, now that you mention it, I even referred to it myself! *laugh*

Tomazas77 12-Jan-12 11:29am

I've just added this file so is not linked anywhere yet, but insede file is linked in cString cPlainKey::ToString(bool hide)
I can copy rest of code ("type,IdSize(),id,&PrintKeyNr()") but this should not be a problems as all of them return int.

Stefan_Lang 12-Jan-12 12:07pm

If those are all int, then your format specifieers should be integral ones, not string! While this has nothing to do with the linker error, I suggest you rewrite that function - and before you do, read up on format specifiers!

Solution 6

The error is that you didn't define cPlainKey::Print.

If all the implementations of "Print" lie in derived classes, just declare it abstract (=0). If not, you must define it (even as {}).

The difference is that is you declare it as abstract, derived classes MUST provide an implementation of Print. If you define it as {}, derived classes don't need to implement Print.
It's useful when you have a lot of derived classes that don't use certain parent functions.

About the code, I agree with all said on "Solution 4". Even if the code links, it contains a lot of things to fix.

Posted 12-Jan-12 5:58am

ErnestoNet

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Stefan_Lang · Accepted Answer · 2012-01-12T05:45:00

Adding this as a new solution as this only addresses the Linker error, not all the other things I mentioned in my previous solution:

First, the linker error indicates there is no implementation for cPlainKey::Print(void). Since this function is not indicated as pure (you commented out the '=0' part), the linker will need this implementation if your code instantiates any object of cPlainKey, or a class derived from cPlainKey.

Solution
1. uncomment the '=0', i. e. make that function pure again. Is there a reason you commented that out? If so you have to fix that, not make the function concrete when it shouldn't be.
2. if you can provide a sensible implementation for cPlainKey::Print(), do that.
(you could technically do both, but it's rarely sensible to provide an implementation to a pure function and I doubt you intended that)

Second, you provided an implementation for cPlainKey::ToString(bool), but there is no such function in your class declaration!? Something isn't right there.

need help on compilation link error LNK2001

6 solutions

Solution 1

Solution 2

Solution 3

Solution 4

Solution 5

Solution 6

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