std::map<int,std::set<std::string> > Wrong? (Segmentation fault.)

[Peter Jansson]

Hello,

I have the following code:

std::map<int,st d::set<std::str ing> > k;
k[0]="1234567890 ";
k[1]="2345678901 ";
//...
std::set<std::s tring> myMethod(std::m ap<int,std::set <std::string> > k)
throw(std::runt ime_error)
{
std::map<int,st d::set<std::str ing> >::const_iterat or i;
i=k.find(0);
if(i==k.end())
throw std::runtime_er ror("No zero in k.");
return i->second;
}

Compilation of this code goes well, but I have the following problem while
executing this in my implementation: "Segmentati on fault". I have
pin-pointed the problem to be the last return statement. When I ignore
using find(int) and instead loops over the map with the following code,
everyting goes fine.

std::set<std::s tring> strings;
for(i=k.begin() ;i!=k.end();i++ )
{
if(k->first==0)
strings=k->second;
}
return strings;

Anybody know what is going on here?

Regards,
Peter Jansson

http://www.jansson.net/

[Ivan Vecerina]

Re: std::map&lt;int ,std::set&lt;st d::string&gt; &gt; Wrong? (Segmentation fault.)

"Peter Jansson" <webmaster@jans son.net> wrote in message
news:Pine.NEB.4 .61.05031408505 20.23649@ukato. freeshell.org.. .[color=blue]
> Hello,
>
> I have the following code:
>
> std::map<int,st d::set<std::str ing> > k;
> k[0]="1234567890 ";
> k[1]="2345678901 ";[/color]
The above two lines are incorrect.
Maybe you meant:
k[0].insert("123456 7890");
k[1].insert("234567 8901");
[color=blue]
> //...
> std::set<std::s tring> myMethod(std::m ap<int,std::set <std::string> > k)[/color]

NB: you probably want to pass the k parameter by const reference:
std::set<std::s tring> myMethod(std::m ap<int,std::set <std::string> > const&
k)
BTW: a typedef of two would probably make sense instead of writing
map<int,set<str ing> > repeatedly...
[color=blue]
> throw(std::runt ime_error)
> {
> std::map<int,st d::set<std::str ing> >::const_iterat or i;
> i=k.find(0);
> if(i==k.end())
> throw std::runtime_er ror("No zero in k.");
> return i->second;
> }[/color]

The above code seems ok, and I don't see a problem in it.
Maybe you could post a complete working sample?


Regards,
Ivan
--
http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form

[Kristo]

Re: std::map&lt;int ,std::set&lt;st d::string&gt; &gt; Wrong? (Segmentation fault.)

On 3/14/2005 4:33 AM, Ivan Vecerina wrote:[color=blue]
> "Peter Jansson" <webmaster@jans son.net> wrote in message
> news:Pine.NEB.4 .61.05031408505 20.23649@ukato. freeshell.org.. .
>[color=green]
>>Hello,
>>
>>I have the following code:
>>
>>std::map<int, std::set<std::s tring> > k;
>>k[0]="1234567890 ";
>>k[1]="2345678901 ";[/color]
>
> The above two lines are incorrect.
> Maybe you meant:
> k[0].insert("123456 7890");
> k[1].insert("234567 8901");[/color]

What's wrong with them? If an object with key x doesn't exist,
operator[] will create a default object (in this case a string) to which
a value (e.g., "1234567890 ") can be safely assigned.

Kristo

[Jeff Schwab]

Re: std::map&lt;int ,std::set&lt;st d::string&gt; &gt; Wrong? (Segmentation fault.)

Kristo wrote:[color=blue]
> On 3/14/2005 4:33 AM, Ivan Vecerina wrote:
>[color=green]
>> "Peter Jansson" <webmaster@jans son.net> wrote in message
>> news:Pine.NEB.4 .61.05031408505 20.23649@ukato. freeshell.org.. .
>>[color=darkred]
>>> Hello,
>>>
>>> I have the following code:
>>>
>>> std::map<int,st d::set<std::str ing> > k;
>>> k[0]="1234567890 ";
>>> k[1]="2345678901 ";[/color]
>>
>>
>> The above two lines are incorrect.
>> Maybe you meant:
>> k[0].insert("123456 7890");
>> k[1].insert("234567 8901");[/color]
>
>
> What's wrong with them? If an object with key x doesn't exist,
> operator[] will create a default object (in this case a string)[/color]

No, in this case a std::set<std::s tring>. Look carefully at the
declaration of k.
[color=blue]
> to which
> a value (e.g., "1234567890 ") can be safely assigned.
>
> Kristo[/color]

[Peter Jansson]

Re: std::map&lt;int ,std::set&lt;st d::string&gt; &gt; Wrong? (Segmentation fault.)


On Mon, 14 Mar 2005, Ivan Vecerina wrote:
[color=blue]
> The above two lines are incorrect.
> Maybe you meant:
> k[0].insert("123456 7890");
> k[1].insert("234567 8901");[/color]

Yes, that is what I meant.
[color=blue][color=green]
>> std::set<std::s tring> myMethod(std::m ap<int,std::set <std::string> > k)
>> throw(std::runt ime_error)
>> {
>> std::map<int,st d::set<std::str ing> >::const_iterat or i;
>> i=k.find(0);
>> if(i==k.end())
>> throw std::runtime_er ror("No zero in k.");
>> return i->second;
>> }[/color]
>
> The above code seems ok, and I don't see a problem in it.
> Maybe you could post a complete working sample?
>[/color]

Well, the non-working code is the myMethod method above (non-working since
it fails while executing, it compiles fine). Below, is the code that
works.

std::set<std::s tring> myMethod_which_ works(std::map< int,std::set<st d::string> > k)
throw(std::runt ime_error)
{
std::map<int,st d::set<std::str ing> >::const_iterat or i;
std::set<std::s tring> strings;
bool haveNotFoundZer o=true;
for(i=k.begin() ;i!=k.end() && haveNotFoundZer o;k++)
{
if(i->first==0)
{
haveNotFoundZer o=false;
strings=i->second;
}
}
if(haveNotFound Zero)
throw std::runtime_er ror("No zero in k.");
return strings;
}

I thought the method find should be more transparent and perhaps even
optimized for sorted maps but it did not work as already mentioned. I
would be grateful for any suggestion/hint on what is wrong.

Regards,
Peter Jansson

http://www.jansson.net/

[Ivan Vecerina]

Re: std::map&lt;int ,std::set&lt;st d::string&gt; &gt; Wrong? (Segmentation fault.)

"Peter Jansson" <webmaster@jans son.net> wrote in message
news:Pine.NEB.4 .61.05031518271 70.3337@norge.f reeshell.org...[color=blue]
> On Mon, 14 Mar 2005, Ivan Vecerina wrote:[color=green]
>> The above code seems ok, and I don't see a problem in it.
>> Maybe you could post a complete working sample?
>>[/color]
>
> Well, the non-working code is the myMethod method above (non-working since
> it fails while executing, it compiles fine). Below, is the code that
> works.[/color]
Again, your usage of the map::find member function seemed correct,
but a problem somewhere else in your code could not be excluded.
And as requested above, *you* should post a minimum code sample
that compiles and reproduces the problem you see.
Something like:

#include <iostream>
#include <map>
#include <set>
#include <string>

std::set<std::s tring>
myMethod(std::m ap<int,std::set <std::string> > const& k)
throw(std::runt ime_error)
{
std::map<int,st d::set<std::str ing> >::const_iterat or i = k.find(0);
if(i==k.end())
throw std::runtime_er ror("No zero in k.");
return i->second;
}

int main()
{
std::map<int,st d::set<std::str ing> > k;
k[0].insert("123456 7890");
k[1].insert("234567 8901");

std::set<std::s tring> set = myMethod(k); // does not throw
std::cout << *set.begin(); // prints "1234567890 "
}
[color=blue]
> I thought the method find should be more transparent and perhaps even
> optimized for sorted maps but it did not work as already mentioned.[/color]
map::find is transparent and optimized, and does work.
You shouldn't persuade yourself otherwise before writing a complete
minimum sample that compiles and illustrates the issue you observe.
[color=blue]
> I would be grateful for any suggestion/hint on what is wrong.[/color]
The above code shall work, and does on the platform I use.
If it fails on your system, this would be a bug in the implementation
you use, and you should seek support from your vendor or a platform-
specific forum (and use the code sample as a bug report).


Ivan
--
http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form