array => vector

[VeganFanatic]

what do I need as an overload= for the array type I have a vector template that needs an overload

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[Stephen Hewitt]

Perhaps this well set you on the right path:

// Console.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <tchar.h>
#include <iostream>

using namespace std;

class MyVector
{
public:
template <typename T, size_t N>
MyVector& operator=(const T(&a)[N])
{
for (size_t i=0; i<N; ++i)
{
cout << a[i] << " ";
}

	cout << endl;

	return \*this;
}

};

int _tmain(int argc, _TCHAR* argv[])
{
MyVector vec;
int n[] = {1, 2, 3, 4};
const char* s[] = {"One", "Two", "Three", "Four"};
vec = n;
vec = s;

cout << endl;

}

Output:

1 2 3 4
One Two Three Four

NOTE: Visual Studio 6 can't handle it.

Steve

[VeganFanatic]

For some reason VS 2010 does not like that. Do I need more assignment overloading? vector operator= (vector &that) { // assignment operator for (int i=0; i < that.data.size(); i++) this->data[i] = that.data[i]; return *this; } vector operator= (base* that) { // assignment operator for (int i=0; i < sizeof(that); i++) this->data[i] = that[i]; return *this; }

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[Stephen Hewitt]

It looks like you need something like this instead of the second overload:

template <std::size_t N>
vector& operator=(const base(&that)[N])
{
for (int i=0; i<N; ++i)
data[i] = that[i];
return *this;
}

sizeof(that) is wrong for may reasons. It's the size of a single base type in bytes. Also, read up on array to pointer decay. NOTE: Both overload should return vector&, not vector. PS: No animals where harmed while posting this code.

Steve

[VeganFanatic]

This variable N, is that second needed? My goal... matrix a; matrix[0] = {0, 1, 4, 1, 9}; matrix[1] = {....}; and so on, so I am trying to get the vector base template working better

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modified on Thursday, June 17, 2010 8:38 PM

[Stephen Hewitt]

I don't think this kind of thing can be done unless you've got some brand spanking new C++0x[^] compliant compiler. Specifically the C++0x "Initializer lists" feature.

Steve

[VeganFanatic]

Guess I am waiting for Visual Studio 2010 SP1

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[Stephen Hewitt]

Have a look at Boost[^]'s Boost.Assign[^] library.

Steve

[VeganFanatic]

I have looked the std::array and I will see what I can do about casting that to my vector template. #include

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[VeganFanatic]

That was another waste of time. Sure seems VC 2010 is hostile to data processing.

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[Aescleal]

If you want to do something with an array and not a pointer to a lump of data then declare the function as:

template <std::size_t N> my_class &operator=(T (&t)[N])

where T is the type you're templating on. Usually what you do is have a copy constructor that takes the same parameters and then you implement operator= in terms of it (which can improve exception saftety as well if you do it right):

template <std::size_t N> my_class &operator=( T (&t)[N] )
{
my_class temp( t );
std::swap( temp. *this );
return *this;
}

The important thing is getting the size of the array into the function. Another way of doing this, which is common in the STL, is to specify a range of interators, in this case you could use a range of T pointers:

my_class &operator=( const T *begin, const T * const end )

I'd strongly recommend you grab a copy of "Exceptional C++" by Herb Sutter - it's got loads of guidance on how to write assignment operators. Cheers, Ash