How to create a class which inheritates from std::vector - c++

I need to inherit all functions from std::vector and I want to overload operators to make a complete matrix class.
There is not too much documentation on this topic.
Matriz.h
#include <vector>
#include <iostream>
using namespace std;
template<typename T>
class Matriz:vector<T>
{
public:
using vector<T>::vector;
private:
}
Matriz.cpp
int main()
{
Matriz<int> dani;
dani.push_back(2); //Here is the error and I don`t know what it happens
}
When I want to initialize it, I got an error.
Severity Code Description Project File Line Suppression State
Error C2247 'std::vector<int,std::allocator<_Ty>>::push_back' not accessible because 'Matriz<int>' uses 'private' to inherit from 'std::vector<int,std::allocator<_Ty>>'

This should work:
#include <vector>
#include <iostream>
template<typename T>
class Matriz: public std::vector<T>
{
public:
using std::vector<T>::vector;
private:
};
int main()
{
Matriz<int> dani;
dani.push_back(2);
dani.push_back(3);
for(const auto& it: dani)
std::cout << it << " ";
}

Inherit from vector class is a mistake
It is very difficult and produces a lot of errors as it is said here.
I have made a class which has a vector and inlcudes:
template
operator overloading
matrix operations
LINK : vector.h
#pragma once
#include <vector>
#include <iostream>
template<class T>
class Vector
{
public:
Vector();
Vector(int);
Vector(int, int);
~Vector();
std::vector<std::vector<T>> v;
bool Check_Size() ;
template<typename T1> bool Check_Size(std::vector<T1>&) ;
template<typename T1> bool Check_Size_Fast(std::vector<T1>&);
void Print();
void Transponse();
void Inverse();
void Inverse2();
void Inverse3();
template<class T,class Q>
friend std::vector<std::vector<T>> operator* (const Q , Vector<T> );
template<class T,class Q>
friend std::vector<std::vector<T>> operator* (Vector<T> , const Q );
template<class T>
friend std::vector<std::vector<T>> operator*(Vector<T>& , Vector<T>&);
template<typename T>
friend std::vector<std::vector<T>> operator+(Vector<T> &, Vector<T> &);
template<typename T>
friend std::vector<std::vector<T>> operator-(Vector<T> &, Vector<T> &);
Vector<T>& operator = (const std::vector<std::vector<T>>& v)
{
this->v = v;
return *this;
}
std::vector<std::vector<T>>& operator +=( Vector<T>&v) {
return v + (*this);
}
std::vector<std::vector<T>>& operator -=(Vector<T>&v) {
return v - (*this);
}
std::vector<std::vector<T>>& operator *=(Vector<T>&v) {
return v * (*this);
}
private:
void Recursive_Check(std::vector<T>&);
};

Related

Overriding << operator for templated struct

numcpp.h file
#include "iostream"
namespace numcpp{
template<typename T>
struct Vector
{
std::vector<T> v;
};
template<typename T>
struct Matrix
{
std::vector<T> m;
//template<typename T>
friend std::ostream& operator << (std::ostream& out, const mf& mat);
};
typedef Vector<float> vf;
typedef Matrix<vf> mf;
}
I am trying to overload << operator for cout to be able to print mf. First I tried making the overloading function a friend that directly takes mf as argument. I did this because if I took Matrix as argument, I would need to deal with template and I don't know how to do that.
numcpp.cpp file
#include "numcpp.h"
namespace numcpp{
std::ostream& operator << (std::ostream& out, const mf& mat)
{
//overloaded out here
return out;
}
}
main.cpp
#include "iostream"
#include "numcpp.h"
int main()
{
numcpp::mf inputs;
// inputs is filled with random numbers here
std::cout << inputs;
}
But this gives an error identified mf is undefined in .h file in line friend std::ostream& operator << (std::ostream& out, const mf& mat);
So I ditched this approach and tried removing the friend function declaration from Matrix without changing the .cpp file. But now I get a different error saying no operator << matches these operands.
I think this is because the overload is done in numcpp namespace so it is not visible from main which is outside the namesapce.
What you normally want is to define a template in your header file. The definition needs to be available at the call-site to allow the compiler to make an instatiation of the template.
If possible, the easiest way is to put the definition in the class definition.
template<typename T>
struct Matrix
{
std::vector<T> m;
// using Matrix here is allowed and refers to the current instatiation, equivalent to writing Matrix<T>
friend std::ostream& operator << (std::ostream& out, const Matrix& mat) {
...
return out;
}
};
Try change your numcpp.h to
namespace numcpp{
template<typename T>
struct Vector
{
std::vector<T> v;
};
typedef Vector<float> vf;
template<typename T>
struct Matrix
{
std::vector<T> m;
//template<typename T>
inline friend std::ostream& operator << (std::ostream& out, const Matrix<vf>& mat);
};
inline std::ostream& operator << (std::ostream& out, const Matrix<vf>& mat)
{
//overloaded out here
return out;
}
typedef Matrix<vf> mf;
}
You are getting this error because mf was not declared when you trying to use it.
Also, you can add the body of the function directly in the definition to get rid of the inline.
The typedefs are not available inside the definition of your class Matrix. You can either declare the typedef before the class definition (#Alloces' answer) of just template the overloaded operator:
#include <vector>
#include <sstream>
#include <iostream>
namespace numcpp {
template<typename T>
struct Vector
{
std::vector<T> v;
};
template<typename T>
struct Matrix
{
std::vector<T> m;
template<typename K> // template parameter must not be named T
inline friend std::ostream& operator << (std::ostream& out, const Matrix<K>& mat);
};
template<typename K>
inline std::ostream& operator << (std::ostream& out, const Matrix<K>& mat)
{
return out << "Just a test";
}
typedef Vector<float> vf;
typedef Matrix<vf> mf;
}
int main() {
numcpp::mf inputs;
std::cout << inputs << "\n"; // Just a test
}

using vector in ostream overload friend function

I have a template class called "KeyedCollection" that contains functions to insert data into a vector, as well as stream out the data. The vector is a private member function. I can't seem to figure out how to use the information from this vector in my overloading ostream friend function. Note: I cannot change the general structure of the class and the function arguments, they have to stay as they are. I list all of the class for reference, but the function in question is the last one.
#include "stdafx.h"
#include <iostream>
#include <vector>
#include "Windows.h"
#include <string>
using namespace std;
template <class K, class T>
class KeyedCollection {
public:
// Create an empty collection
KeyedCollection();
// Return the number of objects in the collection
int size() const;
// Insert object of type T with a key of type K into the
// collection using an “ignore duplicates” policy
void insert(const K&, const T&);
// Output data value of objects in the collection,
// one data value per line
friend ostream& operator<<(ostream&,
const KeyedCollection&);
private:
// Insert required members here
int objSize;
vector<T> objects;
};
template<class K, class T>
KeyedCollection<K,T>::KeyedCollection() {
objSize = 0;
vector<T> objects;
}
template<class K, class T>
int KeyedCollection<K,T>::size() const {
objSize = objects.size();
return objSize;
}
template<class K, class T>
void KeyedCollection<K,T>::insert(const K&,const T& c) {
objects.push_back(c);
}
// !!! function i am trying to define !!!
template<class K, class T>
ostream& operator<<(ostream& outstream,const KeyedCollection<K,T>& inst) {
outstream<<inst<<endl;
return outstream;
}
Also, I'm getting an error that says
"fatal error LNK1120: 1 unresolved externals"
and one that says
"error LNK2019: unresolved external symbol "class std::basic_ostream > & __cdecl operator<<(class std::basic_ostream > &,class KeyedCollection const &)" (??6#YAAAV?$basic_ostream#DU?$char_traits#D#std###std##AAV01#ABV?$KeyedCollection#HVCustomer#####Z) referenced in function _main" ...
Just as a side question, any idea what those could be?
cppreference and Johannes Schaub - litb both provide the same method for getting this to work.
You want to make one single instance (called "specialization" in
generic terms) of that template a friend. You do it the following way
[...]
First make a forward declaration before the definition of your class:
template <class K, class T> class KeyedCollection;
template<class K, class T>
ostream& operator<<(ostream& outstream,const KeyedCollection<K,T>& inst);
Because the compiler knows from the parameter list that the template
arguments are T and U, you don't have to put those between <...>, so
they can be left empty.
Then make your friend declaration and be sure to add <> after operator<<:
template <class K, class T>
class KeyedCollection {
public:
// snip
friend ostream& operator<< <> (ostream& outstream,const KeyedCollection<K,T>& inst);
// snip
};
Finally you can define it:
template<class K, class T>
ostream& operator<<(ostream& outstream,const KeyedCollection<K,T>& inst) {
// Just an example
for (const auto& t : inst.objects)
{
std::cout << t << std::endl;
}
return outstream;
}
Live Example
Alternately, do what Yakk suggested.
template <class K, class T>
class KeyedCollection {
public:
// snip
friend ostream& operator<<(ostream& outstream,const KeyedCollection<K,T>& inst) {
for (const auto& t : inst.objects)
{
std::cout << t << std::endl;
}
return outstream;
}
// snip
};
Live Example

Why would this template not compile?

I have a pretty simple template which is a container which is an array of T. I am getting a syntax error :
container.h(7): error C2143: syntax error : missing ';' before '&'. I have tried removing the declaration there but then the error just skips over to the definition. Would appreciate any help.
EDIT: now i fixed the using namespace thing, but another error popped:
container.h(8): error C2975: 'Container' : invalid template argument for 'unnamed-parameter', expected compile-time constant expression
#include <typeinfo.h>
#include <assert.h>
#include <iostream>
#pragma once
using namespace std;
template <typename T, int> class Container;
template <typename T, int> ostream& operator<< <>(ostream &, const Container<T,int> &);
template<class T , int capacity=0> class Container
{
//using namespace std;
private:
T inside[capacity];
public:
Container()
{
}
~Container(void)
{
}
void set(const T &tType, int index)
{
assert(index>=0 && index<= capacity);
inside[index] = tType;
}
T& operator[](int index)
{
assert(index>=0 && index<= capacity);
return inside[index];
}
friend ostream& operator<< <>(ostream& out, const Container<T,int> c);
{
for(int i=0;i<sizeof(inside)/sizeof(T);i++)
out<<c.inside[i]<< "\t";
return out;
}
};
You probably want:
template <typename T, int N>
ostream& operator<<(ostream &, const Container<T,N> &);
// ^ here you need N, not int!
or, since you don't actually need the forward declaration, you can simply use this implementation in your class:
friend ostream& operator<<(ostream & out, const Container<T,capacity>& c)
{
for(int i=0;i<capacity;++i)
out<<c.inside[i]<< "\t";
return out;
}
You want something like:
template <typename T, int N>
friend ostream& operator<<(ostream & out, const Container<T,N>& c) {
for(int i=0;i<sizeof(inside)/sizeof(T);i++)
out<<c.inside[i]<< "\t";
return out;
}

Template specialization: Is not a Template

Can anyone help me understand why I am getting the following error?
'vcr’ is not a template
Here is the template class declaration:
#include <iostream>
#include <complex>
using namespace std;
template<class T>
class vcr<complex <T> >
{
int length;
complex<T>* vr;
public:
vcr(int, const complex<T>* const);
vcr(int =0, complex<T> =0);
vcr(const vcr&);
~vcr() {delete[] vr;}
int size() const{ return length;}
complex<T>& operator[](int i) const { return vr[i];}
vcr& operator+=(const vcr&);
T maxnorm() const;
template<class S>
friend complex<S> dot(const vcr<complex<S> >&, const vcr<complex<S> >&);
};
template<class T> class vcr<complex <T> >{
... is a partial template specialization. There is a missing general variant, which would (at least) look like this, and which must be visible at the point of the partial specialization:
template<class T> class vcr;
You do not need to provide a body for the general form.

Problems with template in c++ [duplicate]

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Undefined symbol on a template operator overloading function
Here are my source code.
In Number.h
#ifndef NUMBER_H
#define NUMBER_H
#include <iostream>
using std::istream;
using std::ostream;
template <class T> class Number;
template <class T>
ostream& operator<<(ostream&, const Number<T>&);
template <class T>
istream& operator>>(istream&, Number<T>&);
template <class T>
class Number{
public:
Number(const T &n) :i(n) {}
Number() :i(0) {}
T& operator+(const Number&rhs) const;
T& operator-(const Number&rhs) const;
T& operator*(const Number&rhs) const;
T& operator/(const Number&rhs) const;
friend ostream& operator<< <T> (ostream& , const Number<T>&);
friend istream& operator>> <T> (istream& , Number<T>&);
private:
T i;
};
#endif
And in Number.cpp
#include "Number.h"
template<class T>
T& Number<T>::operator+(const Number&rhs) const
{
return i+rhs.i;
}
template<class T>
T& Number<T>::operator-(const Number&rhs) const
{
return i-rhs.i;
}
template<class T>
T& Number<T>::operator*(const Number&rhs) const
{
return i*rhs.i;
}
template<class T>
T& Number<T>::operator/(const Number&rhs) const
{
return i/rhs.i;
}
template<class T>
ostream& operator<<(ostream&os , const Number<T>&rhs)
{
return os<< rhs.i;
}
template<class T>
istream& operator>>(istream&is , Number<T>&rhs)
{
return is >> rhs.i;
}
I cannot find out why there is
undefined reference to `std::istream& operator>><double>(std::istream&,Number<double>&)'
undefined reference to `Number<double>::operator+(Number<double> const&) const'
errors so on so forth
Use .hpp for template and you can't return reference on a temporary object.
number.h
#ifndef NUMBER_H
#define NUMBER_H
#include <iostream>
using std::istream;
using std::ostream;
template <class T> class Number;
template <class T>
ostream& operator<<(ostream&, const Number<T>&);
template <class T>
istream& operator>>(istream&, Number<T>&);
template <class T>
class Number{
public:
Number(const T &n) :i(n) {}
Number() :i(0) {}
T operator+(const Number&rhs) const; // Error Here return T not T&
T operator-(const Number&rhs) const;
T operator*(const Number&rhs) const;
T operator/(const Number&rhs) const;
friend ostream& operator<< <T> (ostream& , const Number<T>&);
friend istream& operator>> <T> (istream& , Number<T>&);
private:
T i;
};
#include <number.hpp>
#endif
number.hpp
#ifndef NUMBER_HPP
#define NUMBER_HPP
template<class T>
T
Number<T>::operator+(const Number& rhs) const
{
return i + rhs.i;
}
template<class T>
T
Number<T>::operator-(const Number&rhs) const
{
return i-rhs.i;
}
template<class T>
T
Number<T>::operator*(const Number&rhs) const
{
return i*rhs.i;
}
template<class T>
T
Number<T>::operator/(const Number&rhs) const
{
return i/rhs.i;
}
template<class T>
ostream& operator<<(ostream&os , const Number<T>&rhs)
{
return os<< rhs.i;
}
template<class T>
istream& operator>>(istream&is , Number<T>&rhs)
{
return is >> rhs.i;
}
#endif
main.cpp
#include <iostream>
#include <number.h>
int
main(int, const char**)
{
Number<double> value(1);
Number<double> add(3);
std::cout << value + add << std::endl;
std::cout << value * add << std::endl;
std::cout << value - add << std::endl;
std::cout << value / add << std::endl;
return 0;
}
The definitions of all those member functions need to be available to any translation unit that instantiates the template. Imagine a file that includes Number.h and attempts to use Number<int>. The compiler then needs to generate all of the code for Number instantiated with T as int. How can it do that if it's only seen Number.h? It doesn't know the definition of the member functions.
The fix is to put the definitions of your member functions (everything from Number.cpp) in Number.h. Alternatively, some people like to name Number.cpp as Number.tpp and, instead of #include "Number.h" in Number.cpp, put #include "Number.tpp" at the bottom of Number.h - basically inverting the inclusion so that the header always includes the implementation.