Can't compile template class

Question

I have try to run a template class with devc++ ver 4.9.9.2 but it didn't work because:

compile log:

//-------------------------------
Compiler: Default compiler
Building Makefile: "H:\BaiTap\Ky6\OPP\Test\Bai3.1_DEVC\Makefile.win"
Finding dependencies for file: H:\BaiTap\Ky6\OPP\Test\Bai3.1_DEVC\main.cpp
Finding dependencies for file: H:\BaiTap\Ky6\OPP\Test\Bai3.1_DEVC\Vecto.cpp
Executing  make...
make.exe -f "H:\BaiTap\Ky6\OPP\Test\Bai3.1_DEVC\Makefile.win" all
g++.exe -c main.cpp -o main.o -I"F:/Dev-Cpp/lib/gcc/mingw32/3.4.2/include"  -I"F:/Dev-Cpp/include/c++/3.4.2/backward"  -I"F:/Dev-Cpp/include/c++/3.4.2/mingw32"  -I"F:/Dev-Cpp/include/c++/3.4.2"  -I"F:/Dev-Cpp/include"   

**F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator_base_types.h: In instantiation of `std::iterator_traits<float>':
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator.h:96:   instantiated from `std::reverse_iterator<float>'
Vecto.h:22:   instantiated from `Vecto<float>'
main.cpp:9:   instantiated from here
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator_base_types.h:129: error: `float' is not a class, struct, or union type
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator_base_types.h:130: error: `float' is not a** class, struct, or union type
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator_base_types.h:131: error: `float' is not a class, struct, or union type
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator_base_types.h:132: error: `float' is not a class, struct, or union type
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator_base_types.h:133: error: `float' is not a class, struct, or union type
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator.h: In instantiation of `std::reverse_iterator<float>':
Vecto.h:22:   instantiated from `Vecto<float>'
main.cpp:9:   instantiated from here

**F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator.h:96: error: no type named `iterator_category' in `struct std::iterator_traits<float>'**
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator.h:103: error: no type named `difference_type' in `struct std::iterator_traits<float>'
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator.h:104: error: no type named `reference' in `struct std::iterator_traits<float>'
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator.h:105: error: no type named `pointer' in `struct std::iterator_traits<float>'
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator.h:150: error: no type named `reference' in `struct std::iterator_traits<float>'
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator.h:162: error: no type named `pointer' in `struct std::iterator_traits<float>'
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator.h:220: error: no type named `difference_type' in `struct std::iterator_traits<float>'
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator.h:229: error: no type named `difference_type' in `struct std::iterator_traits<float>'
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator.h:241: error: no type named `difference_type' in `struct std::iterator_traits<float>'
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator.h:250: error: no type named `difference_type' in `struct std::iterator_traits<float>'
F:/Dev-Cpp/include/c++/3.4.2/bits/stl_iterator.h:262: error: no type named `reference' in `struct std::iterator_traits<float>'
Vecto.h: In instantiation of `Vecto<float>':
main.cpp:9:   instantiated from here
Vecto.h:22: error: template-id `operator+<float>' for `Vecto<float> operator+(const Vecto<float>&, const Vecto<float>&)' does not match any template declaration
Vecto.h:24: error: template-id `operator-<float>' for `Vecto<float> operator-(const Vecto<float>&, const Vecto<float>&)' does not match any template declaration
Vecto.h:33: error: template-id `operator<< <float>' for `std::basic_ostream<char, std::char_traits<char> >& operator<<(std::basic_ostream<char, std::char_traits<char> >&, const Vecto<float>&)' does not match any template declaration
Vecto.h:35: error: templ
........................
make.exe: *** [main.o] Error 1
Execution terminated
//---------------------------------

and here is my code

//-----------------------------------
#ifndef VECTO_H_
#define VECTO_H_

#include  < iostream > 

using namespace std;

template  < class T > 
class Vecto {
private:
    int n;

    T *data;
public:
    // constructor
    Vecto(int = 0);
    // copy constuctor
    Vecto(const Vecto&);
    // destructor
    ~Vecto();

    friend Vecto operator+  < T > (const Vecto &lvt, const Vecto &rvt);

    friend Vecto operator-  < T > (const Vecto &lvt, const Vecto &rvt);

    template  < class U > 
    friend  U operator* (const Vecto < U >  &lvt, const Vecto < U >  &rvt);

    const Vecto &operator= (const Vecto &);

    T &operator[] (int) const;

    friend ostream &operator <<   < T > (ostream &,const Vecto &);

    friend istream &operator >>   < T > (istream &,Vecto &);

};
#endif


//-----------------------------


//file Vecto.cpp

#include "Vecto.h"

using namespace std;

template  < class T > 
Vecto < T > ::Vecto(int n){
    this- > n = n;
    data = new T[n];
}

template  < class T > 
Vecto < T > ::Vecto(const Vecto < T >  &vt){
    n = vt.n;
    delete [] data;
    data = new T[n];
    for(int i=n-1; i > =0; i--)
        data[i] = vt.data[i];
}

template  < class T > 
Vecto < T > ::~Vecto(){
    if(data != NULL)
        delete[] data;
}

template  < class T > 
Vecto < T >  operator+ (const Vecto < T >  &lvt, const Vecto < T >  &rvt){
    Vecto < T >  *p = NULL; 
    if(lvt.n == rvt.n){
        p = new Vecto < T > (lvt.n);
        for(int i=0; i  <  lvt.n ; i++)
            p- > data[i] = lvt.data[i] + rvt.data[i];
    }
    return *p;
}
template  < class T > 
Vecto < T >  operator- (const Vecto < T >  &lvt, const Vecto < T >  &rvt){
    Vecto < T >  *p = NULL; 
    if(lvt.n == rvt.n){
        p = new Vecto < T > (lvt.n);
        for(int i=0; i  <  lvt.n ; i++)
            p- > data[i] = lvt.data[i] - rvt.data[i];
    }
    return *p;
}
template  < class T > 
T operator* (const Vecto < T >  &lvt, const Vecto < T >  &rvt){
    T result =0;
    if(lvt.n == rvt.n){
        for(int i = lvt.n -1; i > =0; i--)
            result += (lvt.data[i]*rvt.data[i]);
    }
    return result;
}

template  < class T > 
const Vecto < T >  &Vecto < T > ::operator= (const Vecto < T >  &vt){
    delete []data;
    n = vt.n;
    data = new T[n];
    for(int i=0; i <  n;i++)
        data[i] = vt.data[i];
    return (*this);
}

template  < class T > 
T &Vecto < T > ::operator[] (int i) const{
    T null = 0;
    if(i < 0||i > =n) return null;
    else return data[i];
}
template  < class T > 
ostream &operator <  <  (ostream &out, const Vecto < T >  &vt){
    out  <  <  "Dims of Vecto: " <  <  vt.n  <  <  endl;
    out  <  <  "Data:"  <  <  endl;
    for(int i = 0; i <  vt.n; i++)
        out  <  <  vt.data[i]  <  < " ";
    out  <  <  endl;
    return out;
}
template  < class T > 
istream &operator >  >  (istream &in, Vecto < T >  &vt){
    for(int i = 0; i <  vt.n; i++){
        cout  <  <  "Vecto[" <  < i <  < "]=";
        in  >  >  vt.data[i];
    }
    return in;
}
//----------------------------------------------------------
//file main.cpp
#include  < cstdlib > 
#include  < iostream > 
#include "Vecto.h"

using namespace std;

int main(int argc, char *argv[])
{
    Vecto < float >  vt1(2);
    cin  >  >  vt1;
    Vecto < float >  vt2 = vt1;// - vt1;
    vt2[0] = 100;
    cout  <  <  vt2;
    cout  <  <  vt2*vt1 <  <  endl;
    system("PAUSE");
    return EXIT_SUCCESS;
}
//--------------------------------

you can download code here.

http://www.mediafire.com/?3hknr5kj33mh4h8 can any one help me? thank for reading this post.

Answer 1

You should be more careful in formatting your code. Things like this

cout < < "Hello" < < endl;

simply do not work – how shall the compiler know that you want to call operator<< and not a misused form of operator< ?

Also, this

friend Vecto operator+<T> (const Vecto &lvt, const Vecto &rvt);

Doesn't make any sense. I assume you want this:

friend Vecto<T> operator+(const Vecto<T> &lvt, const Vecto<T> &rvt);

And, why do you call your class Vecto ? You rather shall call it Vector or even better use std::vector .

Answer 2

Templates must be defined in all translation units where they are to be used. This effectively means that you must define the whole class in the header.