cast operator

[Ali R.]

Hi guys,

I have a string class, which is a wrapper for a char *
with a few operators, like +
What I am trying to do is reduce the number of overloaded operators
so for insteance

class String
{
friend String operator + (const String &Left,const char *Right);
friend String operator + (const char *Left,const String &Right);

//It would be nice if I could avoid this
friend String operator + (const String &Left,const String &Right);

private:
char *m_Buffer;
}

It would be nice if I could avoid this
friend String operator + (const String &Left,const String &Right);
since String can be easily substituded with a char *

a line like this

String Str1("Test");
String Str2("Test");

String Res = Str1 + Str2;

should be able to call this version, if the compiler could automatically
cast the string object into a char *
friend String operator + (const String &Left,const char *Right);

is there a way I can define a cast operator for this class, like
class String
{
public
operator const char *() const { return m_Buffer; }
private:
char *m_Buffer;
}

so that I can do things like the + above, it would work?

I know I have seen this done somewhere, but I can figure out how they did
it.
What I get is an error on the cout line saying

Thanks Ali

[Carl Ribbegaardh]

Re: cast operator

How about writing a constructor that takes a char[] ?
Then the char[] would be converted into a String, and all you need would be
an operator + for 2 Strings. :)

....i hope.

/Carl

"Ali R." <nospam@nospam. com> wrote in message
news:11vYb.207$ xD6.30181429@ne wssvr11.news.pr odigy.com...[color=blue]
> Hi guys,
>
> I have a string class, which is a wrapper for a char *
> with a few operators, like +
> What I am trying to do is reduce the number of overloaded operators
> so for insteance
>
> class String
> {
> friend String operator + (const String &Left,const char *Right);
> friend String operator + (const char *Left,const String &Right);
>
> //It would be nice if I could avoid this
> friend String operator + (const String &Left,const String &Right);
>
> private:
> char *m_Buffer;
> }
>
> It would be nice if I could avoid this
> friend String operator + (const String &Left,const String &Right);
> since String can be easily substituded with a char *
>
> a line like this
>
> String Str1("Test");
> String Str2("Test");
>
> String Res = Str1 + Str2;
>
> should be able to call this version, if the compiler could automatically
> cast the string object into a char *
> friend String operator + (const String &Left,const char *Right);
>
> is there a way I can define a cast operator for this class, like
> class String
> {
> public
> operator const char *() const { return m_Buffer; }
> private:
> char *m_Buffer;
> }
>
> so that I can do things like the + above, it would work?
>
> I know I have seen this done somewhere, but I can figure out how they did
> it.
> What I get is an error on the cout line saying
>
> Thanks Ali
>
>[/color]

[Ron Natalie]

Re: cast operator


"Ali R." <nospam@nospam. com> wrote in message news:11vYb.207$ xD6.30181429@ne wssvr11.news.pr odigy.com...[color=blue]
> Hi guys,
>
> I have a string class, which is a wrapper for a char *
> with a few operators, like +[/color]

Sounds like what you want is a converting constructor, like the std::string
class has.

class String {
public:
String(const char*);
String();
....
};

Then you pretty much give a const char* to anything expecting a String and it will
be converted.

The operator char*() you defined does the opposite (and is probably ill-advised).
It converts you String class to a const char*.

[Jonathan Turkanis]

Re: cast operator

"Ali R." <nospam@nospam. com> wrote in message
news:11vYb.207$ xD6.30181429@ne wssvr11.news.pr odigy.com...[color=blue]
> Hi guys,
>
> I have a string class, which is a wrapper for a char *
> with a few operators, like +
> What I am trying to do is reduce the number of overloaded operators
> so for insteance
>
> class String
> {
> friend String operator + (const String &Left,const char *Right);[/color]

This is the one you can get rid of easily, by providing a non-explicit
String constructor taking a const char*. That's how the standard
library does it:

String(const char*);

[color=blue]
> <snip>
> is there a way I can define a cast operator for this class, like
> class String
> {
> public
> operator const char *() const { return m_Buffer; }
> private:
> char *m_Buffer;
> }[/color]

This should work. There are some well-known problems that can arise
with conversion operators, which you can find discussed in books like
Effective C++, Modern C++ Design, ... (and maybe also the FAQ for this
group.) This is why the standard library uses converting constructors
but explicit member functions (c_str() and data()) for converting to
const char*.
[color=blue]
> What I get is an error on the cout line saying
>
> Thanks Ali[/color]

I wish my compiler knew my name, and was so polite!

Jonathan

[Ali R.]

Re: cast operator

"Jonathan Turkanis" <technews@kanga roologic.com> wrote in message
news:c0tvfv$1c1 osr$1@ID-216073.news.uni-berlin.de...[color=blue]
> "Ali R." <nospam@nospam. com> wrote in message
> news:11vYb.207$ xD6.30181429@ne wssvr11.news.pr odigy.com...[color=green]
> > Hi guys,
> >
> > I have a string class, which is a wrapper for a char *
> > with a few operators, like +
> > What I am trying to do is reduce the number of overloaded operators
> > so for insteance
> >
> > class String
> > {
> > friend String operator + (const String &Left,const char *Right);[/color]
>
> This is the one you can get rid of easily, by providing a non-explicit
> String constructor taking a const char*. That's how the standard
> library does it:
>
> String(const char*);
>
>[color=green]
> > <snip>
> > is there a way I can define a cast operator for this class, like
> > class String
> > {
> > public
> > operator const char *() const { return m_Buffer; }
> > private:
> > char *m_Buffer;
> > }[/color]
>
> This should work. There are some well-known problems that can arise
> with conversion operators, which you can find discussed in books like
> Effective C++, Modern C++ Design, ... (and maybe also the FAQ for this
> group.) This is why the standard library uses converting constructors
> but explicit member functions (c_str() and data()) for converting to
> const char*.
>[color=green]
> > What I get is an error on the cout line saying
> >
> > Thanks Ali[/color]
>[/color]
LOL, I fogot to cut and paste the error line! And I can't type today
[color=blue]
> I wish my compiler knew my name, and was so polite!
>
> Jonathan
>
>
>[/color]

[Ali R.]

Re: cast operator

Thanks Guys,

Ali

"Ali R." <nospam@nospam. com> wrote in message
news:11vYb.207$ xD6.30181429@ne wssvr11.news.pr odigy.com...[color=blue]
> Hi guys,
>
> I have a string class, which is a wrapper for a char *
> with a few operators, like +
> What I am trying to do is reduce the number of overloaded operators
> so for insteance
>
> class String
> {
> friend String operator + (const String &Left,const char *Right);
> friend String operator + (const char *Left,const String &Right);
>
> //It would be nice if I could avoid this
> friend String operator + (const String &Left,const String &Right);
>
> private:
> char *m_Buffer;
> }
>
> It would be nice if I could avoid this
> friend String operator + (const String &Left,const String &Right);
> since String can be easily substituded with a char *
>
> a line like this
>
> String Str1("Test");
> String Str2("Test");
>
> String Res = Str1 + Str2;
>
> should be able to call this version, if the compiler could automatically
> cast the string object into a char *
> friend String operator + (const String &Left,const char *Right);
>
> is there a way I can define a cast operator for this class, like
> class String
> {
> public
> operator const char *() const { return m_Buffer; }
> private:
> char *m_Buffer;
> }
>
> so that I can do things like the + above, it would work?
>
> I know I have seen this done somewhere, but I can figure out how they did
> it.
> What I get is an error on the cout line saying
>
> Thanks Ali
>
>[/color]