asked on

Overload operator+ in c++ with wxWindows

[i'm sorry for my English]

Hi!
I really need to solve my problem in few hours... it's very important for me!!!
Please... help me!!! i hope u can help me...

My code is in c++ and i used wxwidgets to make my prog run in a frame/window dialog...
I use dev-cpp with all libreries... and when i compile my code i have no errors, my code works great... but i have a great problem.
I use three text control to do some math operation:

First wxTextCtrl is named wxEdit1.
Second wxTextCtrl is named wxEdit2.
Third wxTextCtrl is named wxEdit3.

1. I convert the content of the first two wxTextCtrl to int or float
2. I add the content of wxEdit1 to wxEdit2 (wxEdit1 + wxEdit2)
3. I display the correct result in wxEdit3

i use template to manage different kind of data.

This is a screenshot of the situation:
http://lnx.mangaitalia.net/question1.gif

the code i wrote is this:

[code]
class MyStringClass: public wxString
{
public:
template <class T> bool From_String(T &aValue, const std::string &aStr);
template <class T> std::string To_String(T aValue);
MyStringClass &operator + (const MyStringClass &o);
};

template <class T>
bool MyStringClass::From_String(T &aValue, const std::string &aStr)
{
std::stringstream string(aStr);
return string >> aValue;
}

template <class T>
std::string MyStringClass::To_String(T aValue)
{
std::stringstream string;
string << aValue;
return string.str();
}
[/code]

and i add the values with:

[code]
void Frame::OnButtonAdd(wxCommandEvent& WXUNUSED(event))
{
std::string numero1;
std::string numero2;

MyStringClass var;

//uso il template per gestire le stringhe e convertirle in interi o float!

num1 = wxEdit1->GetValue();

num2 = wxEdit2->GetValue();

if(var.From_String(b, num1) && var.From_String(c, num2)) {
std::string res = var.To_String((b + c));
wxEdit3->SetValue(res.c_str());
}
...
...
...
[/code]

Now... i need to overload the operator+ in order to add "+2" everytime my code try to add wxEdit1+wxEdit2 or to do others sums.
Here is an example:

wxEdit1 = 4;
wxEdit2 = 8;

the sum must to be: wxEdit1 + wxEdit2 + 2 = 4 + 8 + 2 = 14

i must to do this by using the overload of operator+.

i tried to do this:

[code]
MyStringClass &MyStringClass::operator + (const MyStringClass &o)
{
const std::string string;
MyStringClass hope;
std::string hope_work(o);

// hope_work << o;

double b,c;

if(hope.From_String(b, string) && hope.From_String(c, hope_work))
{
std::string res1= hope.To_String((string + hope_work)+2);
}

return *this;
}
[/code]

Dev-Cpp gives me no errors, but the overload doesn't work because i don't know what excatly write to overload the operator and i don't know what value to return to make it wroks well...

Can u help me, please?
i really need to solve this problem in few hours...
please...

Thanks for All!

AlexFM

Can you show client code which should use operator+ ? If you want to add 2, you need operator+(int).

Axter

Hi roccogalati,
> Dev-Cpp gives me no errors, but the overload doesn't work because i
> don't know what excatly write to overload the operator and i don't know
> what value to return to make it wroks well...
Can you please give us more details on how it doesn't work?
What doesn't it do, and what are you expecting it to do?

David Maisonave (Axter)
Cheers!

itsmeandnobodyelse

Try

MyStringClass &MyStringClass::operator + (const MyStringClass &o)
{
int a, b;
if (From_String(a, *this) && From_String(b, o))
return To_String(a+b).c_str();
return "";
}

To add the +2 you might use another overload

MyStringClass &MyStringClass::operator + (int b)
{
int a;
if (From_String(a, *this))
return To_String(a+b).c_str();
return "";
}

You should be able to use it like

std::string res = var.To_String((b + c + 2));
wxEdit3->SetValue(res.c_str());

Note, normally operator+ would concatinate strings rather than convert them to integers and add them.

Note, you shouldn't have to use std::string as type "between". Actually, if your MyStringClass could be converted to const char* and vice versa you don't need std::string.

Regards, Alex

Axter

The following is the recommended approach to overloading arithmetic and assignment operators:

T& T::operator+=(const T&){
//.... impl
return *this
}

T operator+(const T& lhs, const T& rhs){
T temp(lhs);
return temp += rhs;
}

Axter

Notice in my above example, that operator+() function is not a member, and instead it's a global function.
I recommend you make these functions inline functions and declare and implement them within your MyStringClass class declaration.
Example

class MyStringClass
{
///.... impl
publicL:
template<class T>
MyStringClass& operator+=(const T& src){
*this = To_String(*this) + To_String(src);
return *this
}
};

Axter

Here's example for operator+()

The following would be declared outside of your MyStringClass class declaration, and it would not be a member, and instead a global function.

template<class T>
MyStringClass operator+(const MyStringClass& lhs, const T& rhs){
MyStringClass temp(lhs);
return temp += T;
}