| Topic: |
DEVELOP > c-Plus-Plus |
| User: |
"thinktwice" |
| Date: |
16 Aug 2006 03:21:47 AM |
| Object: |
question about using template class |
can't compile the file below, i have remarked the error line, if i
delete that line , it just pass throgh the compile, can anyone tell me
why?
#include "stdafx.h"
#include <iostream>
#include <vector>
using namespace std;
#define pTC static_cast<TClass*>(this);
template<class TClass>
class Base
{
public :
void Test(){
pTC->Hello();
}
void Test(int i){
cout<<"base";
}
};
template<class TClass>
class Derived: public Base<TClass>
{
public :
void Test(){
pTC->Hello(); //error C2143: syntax error : missing ';' before '->'
cout<<"Derived";
}
virtual void Hello(){
cout<<"";
}
};
class Final : public Derived<Final>
{
public:
void Hello(){
cout<< "final";
}
};
int APIENTRY WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
int nCmdShow)
{
// TODO: Place code here.
Final f;
std::vector<int> vec;
f.Test();
return 0;
}
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| User: "Frederick Gotham" |
|
| Title: Re: question about using template class |
16 Aug 2006 09:58:52 AM |
|
|
thinktwice posted:
can't compile the file below, i have remarked the error line, if i
delete that line , it just pass throgh the compile, can anyone tell me
why?
The following compiles without error or warning on my system. I didn't
bother to check the quality of the code however:
#include <iostream>
#include <vector>
using namespace std;
#define pTC (static_cast<TClass*>(this))
template<class TClass>
class Base {
public:
void Test()
{
pTC->Hello();
}
void Test(int)
{
cout << "Base\n";
}
};
template<class TClass>
class Derived: public Base<TClass> {
public:
void Test()
{
pTC->Hello();
cout << "Derived\n";
}
virtual void Hello()
{
}
};
class Final : public Derived<Final> {
public:
void Hello()
{
cout<< "Final";
}
};
int main()
{
Final f;
std::vector<int> vec;
f.Test();
return 0;
}
--
Frederick Gotham
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| User: "Ian Collins" |
|
| Title: Re: question about using template class |
16 Aug 2006 03:49:12 AM |
|
|
thinktwice wrote:
can't compile the file below, i have remarked the error line, if i
delete that line , it just pass throgh the compile, can anyone tell me
why?
#include "stdafx.h"
#include <iostream>
#include <vector>
using namespace std;
#define pTC static_cast<TClass*>(this);
Why are you dong this?
--
Ian Collins.
.
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|
|
| User: "Gary li" |
|
| Title: Re: question about using template class |
16 Aug 2006 04:24:10 AM |
|
|
should remove ; from the macro.
Ian Collins wrote:
thinktwice wrote:
can't compile the file below, i have remarked the error line, if i
delete that line , it just pass throgh the compile, can anyone tell me
why?
#include "stdafx.h"
#include <iostream>
#include <vector>
using namespace std;
#define pTC static_cast<TClass*>(this);
Why are you dong this?
--
Ian Collins.
.
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|
| User: "" |
|
| Title: Re: question about using template class |
16 Aug 2006 03:45:50 AM |
|
|
thinktwice wrote:
can't compile the file below, i have remarked the error line, if i
delete that line , it just pass throgh the compile, can anyone tell me
why?
Yes - it doesn't make sense at all.
#include "stdafx.h"
#include <iostream>
#include <vector>
using namespace std;
#define pTC static_cast<TClass*>(this);
Avoid macros. They just add confusion, and in this case you were so
confused
you didn't see the error.
template<class TClass>
class Base
{
public :
void Test(){
pTC->Hello();
}
void Test(int i){
cout<<"base";
}
};
Wrong - you can't cast a Base<TClass>* to TClass*. You will see this
error if you try to instantiate Base<TClass>::Test()
template<class TClass>
class Derived: public Base<TClass>
{
public :
void Test(){
pTC->Hello(); //error C2143: syntax error : missing ';' before '->'
cout<<"Derived";
}
virtual void Hello(){
cout<<"";
}
};
Same error here.
class Final : public Derived<Final>
{
public:
void Hello(){
cout<< "final";
}
};
int APIENTRY WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
int nCmdShow)
{
// TODO: Place code here.
Final f;
std::vector<int> vec;
f.Test();
return 0;
}
f.Test means f.Derived<Final>::Test(), as Final has no Test function.
So
Derived<Final>::Test is found and instantiated. This will give an
error.
Base<Final>::Test is not instantiated.
HTH,
Michiel Salters
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