getting values in a map - map wrapper class

[Angus]

I am writing a class as a wrapper around a std::map.

The class is:
template<class TKey, class TValue>
class CGeneralMap : protected map<TKey, TValue>

At the moment I have basic functions like Add, Remove etc but I am
really struggling with GetValue, which will be like the value obtained
from [key]

Eg if I create a:
CGeneralMap<int , std::stringTest Map;

and I have a key 3 with std::string value of John. then how in my
GetValue function do I extract the "John"?
In my GetValue function I tried:

value = [3];

but that doesn't work.

[Chris ( Val )]

On Oct 2, 12:28 am, Angus <anguscom...@gm ail.comwrote:

I am writing a class as a wrapper around a std::map.

The class is:
template<class TKey, class TValue>
class CGeneralMap : protected map<TKey, TValue>

At the moment I have basic functions like Add, Remove etc but I am
really struggling with GetValue, which will be like the value obtained
from [key]

Eg if I create a:
CGeneralMap<int , std::stringTest Map;

and I have a key 3 with std::string value of John. then how in my
GetValue function do I extract the "John"?

In my GetValue function I tried:

value = [3];

but that doesn't work.

std::string getKeyValue( int index ) const
{
// Code...

return TestMap[ index ];
}

--
Chris Val

[Angus]

On 1 Oct, 15:38, "Chris ( Val )" <chris...@gmail .comwrote:

On Oct 2, 12:28 am, Angus <anguscom...@gm ail.comwrote:

I am writing a class as a wrapper around a std::map.

The class is:
template<class TKey, class TValue>
class CGeneralMap : protected map<TKey, TValue>

At the moment I have basic functions like Add, Remove etc but I am
really struggling with GetValue, which will be like the value obtained
from [key]

Eg if I create a:
CGeneralMap<int , std::stringTest Map;

and I have a key 3 with std::string value of John. then how in my
GetValue function do I extract the "John"?

In my GetValue function I tried:

value = [3];

but that doesn't work.

std::string getKeyValue( int index ) const
{
// Code...

return TestMap[ index ];
}

--
Chris Val- Hide quoted text -

- Show quoted text -

Yes of course I understand that. But I am talking about from within
my class. From within my GetValue function.

[Chris ( Val )]

On Oct 2, 1:04 am, Angus <anguscom...@gm ail.comwrote:

On 1 Oct, 15:38, "Chris ( Val )" <chris...@gmail .comwrote:

On Oct 2, 12:28 am, Angus <anguscom...@gm ail.comwrote:

I am writing a class as a wrapper around a std::map.

The class is:
template<class TKey, class TValue>
class CGeneralMap : protected map<TKey, TValue>

At the moment I have basic functions like Add, Remove etc but I am
really struggling with GetValue, which will be like the value obtained
from [key]

Eg if I create a:
CGeneralMap<int , std::stringTest Map;

and I have a key 3 with std::string value of John. then how in my
GetValue function do I extract the "John"?

In my GetValue function I tried:

value = [3];

but that doesn't work.

std::string getKeyValue( int index ) const
{
// Code...

return TestMap[ index ];
}

--
Chris Val- Hide quoted text -

- Show quoted text -

Yes of course I understand that. But I am talking about from within
my class. From within my GetValue function.- Hide quoted text -

What am I missing?
What I showed you can be a member function if you put it in a class.

--
Chris Val

[Daniel Kraft]

Angus wrote:

I am writing a class as a wrapper around a std::map.

The class is:
template<class TKey, class TValue>
class CGeneralMap : protected map<TKey, TValue>

At the moment I have basic functions like Add, Remove etc but I am
really struggling with GetValue, which will be like the value obtained
from [key]

Eg if I create a:
CGeneralMap<int , std::stringTest Map;

and I have a key 3 with std::string value of John. then how in my
GetValue function do I extract the "John"?
In my GetValue function I tried:

value = [3];

but that doesn't work.

You could of course use
value = (*this)[3];

But I think the "optimal" solution will be
value = operator[](3);

Both of those call the "operator[]" of the std::map, which is what you want.

Cheers,
Daniel
--
Got two Dear-Daniel-Instant Messages
by MSN, associate ICQ with stress--so
please use good, old E-MAIL!

[yanlinlin82]

"Chris ( Val )" <chris...@gmail .comwrote:

std::string getKeyValue( int index ) const
{
// Code...

return TestMap[ index ];

Can std::map<operat or [](size_t) be used in a const member function?

}

[Angus]

On 1 Oct, 18:32, Daniel Kraft <[e-mail] rote:

Angus wrote:

I am writing a class as a wrapper around a std::map.

The class is:
template<class TKey, class TValue>
class CGeneralMap : protected map<TKey, TValue>

At the moment I have basic functions like Add, Remove etc but I am
really struggling with GetValue, which will be like the value obtained
from [key]

Eg if I create a:
CGeneralMap<int , std::stringTest Map;

and I have a key 3 with std::string value of John. then how in my
GetValue function do I extract the "John"?

In my GetValue function I tried:

value = [3];

but that doesn't work.

You could of course use
value = (*this)[3];

But I think the "optimal" solution will be
value = operator[](3);

Both of those call the "operator[]" of the std::map, which is what you want.

Cheers,
Daniel

--
Got two Dear-Daniel-Instant Messages
by MSN, associate ICQ with stress--so
please use good, old E-MAIL!- Hide quoted text -

- Show quoted text -

Ah brilliant, that is what I needed. But now I have a conversion
problem.

If on line 366 I have:
Value = operator[](Key);

and on line 367 I have:
Value = (*this)[Key];

Then I get these compilation errors in Microsoft Visual C++ version 6:
TestBed.cpp
generalmap.h(36 6) : error C2662: '[]' : cannot convert 'this' pointer
from
'const class CGeneralMap<int ,class std::basic_stri ng<char,struct
std::char_trait s<char>,class std::allocator< char >'

to

'class std::map<int,cl ass std::basic_stri ng<char,struct
std::char_trait s<char>,class std::allocator< char,struct
std::less<int>, class std::allocator< class
std::basic_stri ng<char,struct std::char_trait s<char>,class
std::allocator< char &'

Conversion loses qualifiers
c:\program files\microsoft visual studio\vc98\inc lude
\xmemory(59) : while compiling class-template member function 'void
__thiscall CGeneralMap<int ,class std::basic_stri ng<char,struct
std::char_trait s<char>,class std::allocator< char >::G
etValue(const int,class std::basic_stri ng<char,struct
std::char_trait s<char>,class std::allocator< char &) const'

generalmap.h(36 7) : error C2678: binary '[' : no operator defined
which takes a left-hand operand of type 'const class
CGeneralMap<int ,class std::basic_stri ng<char,struct std::char_trait s<
char>,class std::allocator< char >' (or there is no acceptable
conversion)
c:\program files\microsoft visual studio\vc98\inc lude
\xmemory(59) : while compiling class-template member function 'void
__thiscall CGeneralMap<int ,class std::basic_stri ng<char,struct
std::char_trait s<char>,class std::allocator< char >::G
etValue(const int,class std::basic_stri ng<char,struct
std::char_trait s<char>,class std::allocator< char &) const'

ie I am trying both options.

[Angus]

On 1 Oct, 18:32, Daniel Kraft <[e-mail] rote:

Angus wrote:

I am writing a class as a wrapper around a std::map.

The class is:
template<class TKey, class TValue>
class CGeneralMap : protected map<TKey, TValue>

At the moment I have basic functions like Add, Remove etc but I am
really struggling with GetValue, which will be like the value obtained
from [key]

Eg if I create a:
CGeneralMap<int , std::stringTest Map;

and I have a key 3 with std::string value of John. then how in my
GetValue function do I extract the "John"?

In my GetValue function I tried:

value = [3];

but that doesn't work.

You could of course use
value = (*this)[3];

But I think the "optimal" solution will be
value = operator[](3);

Both of those call the "operator[]" of the std::map, which is what you want.

Cheers,
Daniel

--
Got two Dear-Daniel-Instant Messages
by MSN, associate ICQ with stress--so
please use good, old E-MAIL!- Hide quoted text -

- Show quoted text -

Its ok I had to fiddle with const qualifiers. It now works fine.

[Chris ( Val )]

On Oct 2, 1:04 am, Angus <anguscom...@gm ail.comwrote:

On 1 Oct, 15:38, "Chris ( Val )" <chris...@gmail .comwrote:

On Oct 2, 12:28 am, Angus <anguscom...@gm ail.comwrote:

I am writing a class as a wrapper around a std::map.

The class is:
template<class TKey, class TValue>
class CGeneralMap : protected map<TKey, TValue>

At the moment I have basic functions like Add, Remove etc but I am
really struggling with GetValue, which will be like the value obtained
from [key]

Eg if I create a:
CGeneralMap<int , std::stringTest Map;

and I have a key 3 with std::string value of John. then how in my
GetValue function do I extract the "John"?

In my GetValue function I tried:

value = [3];

but that doesn't work.

std::string getKeyValue( int index ) const
{
// Code...

return TestMap[ index ];
}

Yes of course I understand that. But I am talking about from within
my class. From within my GetValue function.

In future, please try to describe what you're having difficulty
with a bit more clearly. You stated that you were having difficulty
with your member function "GetValue", not operator[] which is quite
different.

While you're at it, ensure that you check for the key's existence.

--
Chris Val

[Chris ( Val )]

On Oct 2, 1:35 am, yanlinli...@gma il.com wrote:

"Chris ( Val )" <chris...@gmail .comwrote:

std::string getKeyValue( int index ) const
{
// Code...

return TestMap[ index ];

Can std::map<operat or [](size_t) be used in a const member function?

I don't think so.

--
Chris Val