Re: std::valarray as value in std::map

From:

Pete Becker <pete@versatilecoding.com>

Newsgroups:

comp.lang.c++

Date:

Mon, 5 Nov 2007 08:22:52 -0500

Message-ID:

<2007110508225275249-pete@versatilecodingcom>

On 2007-11-03 10:20:01 -0400, Chris Forone <4one@gmx.at> said:

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)