Undefined referenceto a Template function in Linux.

rajkar · 03-31-2015, 01:23 AM

hi,
I m using c++ code in Linux OS with gcc compiler.

The class is in Template, the declaration & definition is in header file.
The calling function is in another cpp file.

Ex:template <class T> void samplefunc(T *t, int nbnumb,int ndlay,state *cs,result *rs);//declared in header

template <class T> void samplefunc(T *t, int nbnumb,int ndlay,state *cs,result *rs)//defined in header
{

}
samplefunc(temp->Getp(),temp->nbts,type:

oint,cs,rs);//calling func in cpp file.

ERROR: while calling it , it displays the error like: undefined reference to
'void class name::samplefunc<type>(t*,int,int,cs*,rs*)'

How to solve this issue?...

John VV · 03-31-2015, 02:39 PM

as to your issue ,not sure
BUT
the version of gcc you are using and the Operating system and version would help others

if for example you are using a VERY old version of gcc ( say gcc 3.3 or 4.0 ) the fix might be different than for the NEW gcc4.9

Code:

gcc -V
--- and this ---
uname -a

johnsfine · 03-31-2015, 03:38 PM

I strongly doubt the gcc version or linux version are relevant.

The exact error message and exact code (rather than approximations of each) might help a lot.

Quote:

Originally Posted by rajkar

The class is in Template, the declaration & definition is in header file.
The calling function is in another cpp file.

What hides behind that odd wording? Is there a significant cpp file you haven't mentioned?

Your approximation of the error message makes me guess the compiler had seen the declaration and not the definition, but what you said about hpp contents makes that seem incorrect.
Without exact info, I'm just guessing.

Edit: I just figured out what you are saying and understand the problem and of course the compiler has seen the declaration and not the definition, just as the error message shows. Because you defined a different function than you declared.

The function declaration is inside a class definition, but the function definition is outside the class definition, so it needs to specify className:: to qualify the function name.

Exact (copy paste) of code and messages inside [CODE] blocks in your post would have made all that instantly obvious rather than take guesses at the relationship between what you had done and what you had posted.

rajkar · 04-01-2015, 08:32 AM

hi,
Thanks for ur help... No issues in gcc version.
I m using Template class function in header file which includes a declaration and Implementation.
And calling that function in cpp file(calling function).

ERROR: undefined reference to a function.

Is it clear.. How to solve this?

johnsfine · 04-01-2015, 02:01 PM

Quote:

Originally Posted by rajkar

Is it clear.. How to solve this?

If I correctly estimated what you did from what you posted, then I already told you how to solve it: Add the className:: infront of the function name where you define the function.

If I did not correctly estimate what you did based on what you posted, or if you don't like my advice and hope to get help from someone else, or for any reason want a better answer, you need to post clearer details of what you did and what error message you got.

Quote:

it displays the error like: undefined reference to
'void class name::samplefunc<type>(t*,int,int,cs*,rs*)'

I'd be a lot more sure if you posted exact copy paste of the error message. But in what you posted I see :: where it indicates your function was declared inside a class definition.

Quote:

template <class T> void samplefunc(T *t, int nbnumb,int ndlay,state *cs,result *rs)//defined in header

Again an exact copy/paste of your code inside [CODE] tags would make it a lot easier to be sure we understand what you did. But what you showed was a definition for a function that is not a member of a class, so you did not define the function you declared

johnsfine · 04-01-2015, 02:10 PM

Sample code (untested, I don't have g++ on the computer where I am now):

Code:

class className {
public:
  template <class argType> void fun(argType*);
};
template <class argType> void className::fun(argType*)
{}
int main()
{
  className dummy;
  dummy.fun("something");
  return 0;
}

If you left out the red part in my sample code, I think that creates the error you described, so inserting the equivalent of that red part (with your class name) should fix that.