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I found the following paragraphs from C++ pro Danny Kalev's C++
Reference Guide at
http://www.informit.com/guides/conte...lus&seqNum=206

stating:
__________________________________________________ __________________________________________________ ___________________________________
Let's look at a concrete example of a map that contains a pair of
strings, the first of which is a name and the second one is an e-mail
address. We create the map like this:

#include <map>
#include <string>

map <string, string> emails;
To add an item to a map, use the subscript operator:

emails["J. Horvath"]=""; //#1
If the map already contains the key "J. Horvath", the current
associated value remains unchanged:

emails ["J. Horvath"]=""; //#2 ,has no effect

__________________________________________________ __________________________________________________ ___________________________________

IMHO, this seems wrong. #2 should update the data_value of key "J.
Horvath" to "".

Because I think essentially mymap[k] equals to (*(mymap.insert
(value_type(k, data_type())).first)).second ,which enables #2 to
update the value of key "J. Horvath".

I can not find any contact email of Danny, so I posted this issue
here, I am hoping someone could either confirm I am correct or
opposite.

Any input is appreciated.
Regards,
Gob00st

On Feb 4, 10:36*am, gob0...@googlemail.com wrote:
> emails["J. Horvath"]="jhorv...@mail.com"; //#1
> If the map already contains the key "J. Horvath", the current
> associated value remains unchanged:
>
> emails ["J. Horvath"]="newa...@com.net"; //#2 ,has no effect>
> IMHO, this seems wrong. #2 should update the data_value of key "J.
> Horvath" to "newa...@com.net".
>
> Because I think essentially mymap[k] equals to (*(mymap.insert
> (value_type(k, data_type())).first)).second ,which enables #2 to
> update the value of key "J. Horvath".

You are correct of course. Yikes. That is a rather glaring
misunderstanding of how std::map works (especially for someone writing
articles on the subject!). Something I might dismiss if it was 1994,
but 2004?

Joe C

On Feb 4, 3:45*pm, joec...@gmail.com wrote:
> On Feb 4, 10:36*am, gob0...@googlemail.com wrote:
>
> > emails["J. Horvath"]="jhorv...@mail.com"; //#1
> > If the map already contains the key "J. Horvath", the current
> > associated value remains unchanged:
>
> > emails ["J. Horvath"]="newa...@com.net"; //#2 ,has no effect>
> > IMHO, this seems wrong. #2 should update the data_value of key "J.
> > Horvath" to "newa...@com.net".
>
> > Because I think essentially mymap[k] equals to (*(mymap.insert
> > (value_type(k, data_type())).first)).second ,which enables #2 to
> > update the value of key "J. Horvath".
>
> You are correct of course. * Yikes. *That is a rather glaring
> misunderstanding of how std::map works (especially for someone writing
> articles on the subject!). * Something I might dismiss if it was 1994,
> but 2004?
>
> Joe C

Thanks for the quick reply. I thought I was probably right, its just
Danny is a C++ expert, so I can't be 100% sure.
Looking at his profile, he was once a member of the C++ standards
committee between 1997 and 2000...
Anyway, I am sure I am correct now.
Gob00st

On 4 Feb., 16:36, gob0...@googlemail.com wrote:
> I found the following paragraphs from C++ pro Danny Kalev's C++
> Reference Guide athttp://www.informit.com/guides/content.aspx?g=cplusplus&seqNum=206
>
> stating:
[snipped rubbish]
> Because I think essentially mymap[k] equals to (*(mymap.insert
> (value_type(k, data_type())).first)).second ,which enables #2 to
> update the value of key "J. Horvath".
>

You are correct, of course. Sadly Danny Kalev is not the expert on C++
he claims to be - and he never was. The next time you (and others) see
his name, realise that is he talks about C++ you better not read it.

/Peter

ACCU reviews list as 'Not recommended'

http://accu.org/index.php?module=boo...earch&rid=1170

http://accu.org/index.php?module=boo...search&rid=294

On Feb 4, 7:48*pm, p...@lib.hu wrote:
> ACCU reviews list as 'Not recommended'
>
> http://accu.org/index.php?module=boo...earch&rid=1170
>
> http://accu.org/index.php?module=boo...search&rid=294

Thanks for all your replies, very helpful and not only in C++...
Gob00st