«

Hello group,

g++ (3.4.2, mingw):

float init[] = {1.f, 2.f, 3.f};
std::map<std::string, std::valarray<float> > mp;

mp["name"] = std::valarray(init, 3);
mp["name"].size(); // should be 3, but IS 0!

Do i ignored something? Does map not do a copy of value?

HAND, Chris

Chris Forone schrieb:
> Hello group,
>
> g++ (3.4.2, mingw):
>
> float init[] = {1.f, 2.f, 3.f};
> std::map<std::string, std::valarray<float> > mp;
>
> mp["name"] = std::valarray(init, 3);
> mp["name"].size(); // should be 3, but IS 0!
>
> Do i ignored something? Does map not do a copy of value?
>
> HAND, Chris

compilable:

#include <iostream>
#include <map>
#include <valarray>

int main()
{
float init[] = {1.f, 2.f, 3.f};
std::map<std::string, std::valarray<float> > mp;

mp["name"] = std::valarray<float>(init, 3);

std::cout << mp["name"].size() << std::endl;
}

g++ (4.1.2, ubuntu) has the same behavior...

Chris

Chris Forone schrieb:
> Chris Forone schrieb:
>> Hello group,
>>
>> g++ (3.4.2, mingw):
>>
>> float init[] = {1.f, 2.f, 3.f};
>> std::map<std::string, std::valarray<float> > mp;
>>
>> mp["name"] = std::valarray(init, 3);
>> mp["name"].size(); // should be 3, but IS 0!
>>
>> Do i ignored something? Does map not do a copy of value?
>>
>> HAND, Chris
>
> compilable:
>
> #include <iostream>
> #include <map>
> #include <valarray>
>
> int main()
> {
> float init[] = {1.f, 2.f, 3.f};
> std::map<std::string, std::valarray<float> > mp;
>
> mp["name"] = std::valarray<float>(init, 3);
>
> std::cout << mp["name"].size() << std::endl;
> }
>
> g++ (4.1.2, ubuntu) has the same behavior...
>
> Chris

SOLVED!

..insert does the trick... operator[] only does std-ctor...

HAND, Chris

On 2007-11-03 10:20:01 -0400, Chris Forone <> said:

> Chris Forone schrieb:
>> Chris Forone schrieb:
>>> Hello group,
>>>
>>> g++ (3.4.2, mingw):
>>>
>>> float init[] = {1.f, 2.f, 3.f};
>>> std::map<std::string, std::valarray<float> > mp;
>>>
>>> mp["name"] = std::valarray(init, 3);
>>> mp["name"].size(); // should be 3, but IS 0!
>>>
>>> Do i ignored something? Does map not do a copy of value?
>>>
>>> HAND, Chris
>>
>> compilable:
>>
>> #include <iostream>
>> #include <map>
>> #include <valarray>
>>
>> int main()
>> {
>> float init[] = {1.f, 2.f, 3.f};
>> std::map<std::string, std::valarray<float> > mp;
>> mp["name"] = std::valarray<float>(init, 3);
>> std::cout << mp["name"].size() << std::endl;
>> }
>>
>> g++ (4.1.2, ubuntu) has the same behavior...
>>
>> Chris
>
> SOLVED!
>
> .insert does the trick... operator[] only does std-ctor...
>

No, it doesn't. It just happens to look like it works. The problem has
nothing to do with valarray: you'll see the same behavior with any type
for the value. The problem is in the index, not the value. Quoted
strings are not guaranteed to be unique, so mp["name"] may be a
different map element than some other mp["name"].

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

On Nov 5, 2:22 pm, Pete Becker <p...@versatilecoding.com> wrote:
> On 2007-11-03 10:20:01 -0400, Chris Forone <4...@gmx.at> said:
> > Chris Forone schrieb:
> >> Chris Forone schrieb:
> >>> Hello group,

> >>> g++ (3.4.2, mingw):

> >>> float init[] = {1.f, 2.f, 3.f};
> >>> std::map<std::string, std::valarray<float> > mp;

> >>> mp["name"] = std::valarray(init, 3);
> >>> mp["name"].size(); // should be 3, but IS 0!

> >>> Do i ignored something? Does map not do a copy of value?

> >>> HAND, Chris

> >> compilable:

> >> #include <iostream>
> >> #include <map>
> >> #include <valarray>

> >> int main()
> >> {
> >> float init[] = {1.f, 2.f, 3.f};
> >> std::map<std::string, std::valarray<float> > mp;
> >> mp["name"] = std::valarray<float>(init, 3);
> >> std::cout << mp["name"].size() << std::endl;
> >> }

> >> g++ (4.1.2, ubuntu) has the same behavior...

> > SOLVED!

> > .insert does the trick... operator[] only does std-ctor...

> No, it doesn't. It just happens to look like it works. The
> problem has nothing to do with valarray: you'll see the same
> behavior with any type for the value. The problem is in the
> index, not the value. Quoted strings are not guaranteed to be
> unique, so mp["name"] may be a different map element than some
> other mp["name"].

But his map uses std::string as a key, not char const*, so the
string literal will be converted.

I'm not familiar enough with valarray to really comment, but his
initial use of std::map seems correct: the call to mp["name"]
does insert a valarray constructed withe the default
constructor, before returning a reference to the new object; the
assignment operator then does whatever the assignment operator
for valarray does.

--
James Kanze (GABI Software) email:
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

On 2007-11-05 12:13:44 -0500, James Kanze <> said:

> On Nov 5, 2:22 pm, Pete Becker <p...@versatilecoding.com> wrote:
>
>> No, it doesn't. It just happens to look like it works. The
>> problem has nothing to do with valarray: you'll see the same
>> behavior with any type for the value. The problem is in the
>> index, not the value. Quoted strings are not guaranteed to be
>> unique, so mp["name"] may be a different map element than some
>> other mp["name"].
>
> But his map uses std::string as a key, not char const*, so the
> string literal will be converted.
>

Whoops, sorry about confusing the issue.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)