constructing and initializing a scoped_array

[Dennis Jones]

Hi,

I have some old code that I am refactoring to use smart pointers and have
run into a small problem. My original code looks something like this:

class WorkerThread
{
std::map<int, Handler> &HandlerMap;
public:
WorkerThread( std::map<int, Handler> &AHandlerMap )
: HandlerMap( AHandlerMap ) {}
};

WorkerThread *WorkerThreads[MAXTHREADS];

for ( int i=0; i<MAXTHREADS; i++ )
{
WorkerThreads[i] = new WorkerThread( TheHandlerMap );
}
And I think I'd like to change it to use a scoped_array:

boost::scoped_array< WorkerThread > WorkerThreads;

WorkerThreads( new WorkerThread[/*...*/] )

Unfoortunately, the WorkerThread class does not have a default constructor,
and as such, the compiler does not allow me to cosntruct a scoped_array. So
maybe a scoped_array isn't the way to go, but it seemed like most obvious
choice. What would be an appropriate solution?

Thanks,

- Dennis

[Jonathan Mcdougall]

Dennis Jones wrote:

I have some old code that I am refactoring to use smart pointers and have
run into a small problem. My original code looks something like this:

class WorkerThread
{
std::map<int, Handler> &HandlerMap;
public:
WorkerThread( std::map<int, Handler> &AHandlerMap )
: HandlerMap( AHandlerMap ) {}
};

WorkerThread *WorkerThreads[MAXTHREADS];

for ( int i=0; i<MAXTHREADS; i++ )
{
WorkerThreads[i] = new WorkerThread( TheHandlerMap );
}
And I think I'd like to change it to use a scoped_array:

boost::scoped_array< WorkerThread > WorkerThreads;

WorkerThreads( new WorkerThread[/*...*/] )

Unfoortunately, the WorkerThread class does not have a default constructor,
and as such, the compiler does not allow me to cosntruct a scoped_array. So
maybe a scoped_array isn't the way to go, but it seemed like most obvious
choice. What would be an appropriate solution?

Perhaps I missed something, but what about a std::vector?
Jonathan

[Victor Bazarov]

Dennis Jones wrote:

I have some old code that I am refactoring to use smart pointers and
have run into a small problem. My original code looks something like
this:

class WorkerThread
{
std::map<int, Handler> &HandlerMap;
public:
WorkerThread( std::map<int, Handler> &AHandlerMap )
: HandlerMap( AHandlerMap ) {}
};

WorkerThread *WorkerThreads[MAXTHREADS];

for ( int i=0; i<MAXTHREADS; i++ )
{
WorkerThreads[i] = new WorkerThread( TheHandlerMap );
}
And I think I'd like to change it to use a scoped_array:

boost::scoped_array< WorkerThread > WorkerThreads;

WorkerThreads( new WorkerThread[/*...*/] )

Unfoortunately, the WorkerThread class does not have a default
constructor, and as such, the compiler does not allow me to cosntruct
a scoped_array. So maybe a scoped_array isn't the way to go, but it
seemed like most obvious choice. What would be an appropriate
solution?

I have no idea what 'scoped_array' is (it's not part of the Standard
Library, AFAICT), but can you tell me what's inaproppriate about, say,
'std::vector'?

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[boaz_sade]

Victor Bazarov wrote:

Dennis Jones wrote:

I have some old code that I am refactoring to use smart pointers and
have run into a small problem. My original code looks something like
this:

class WorkerThread
{
std::map<int, Handler> &HandlerMap;
public:
WorkerThread( std::map<int, Handler> &AHandlerMap )
: HandlerMap( AHandlerMap ) {}
};

WorkerThread *WorkerThreads[MAXTHREADS];

for ( int i=0; i<MAXTHREADS; i++ )
{
WorkerThreads[i] = new WorkerThread( TheHandlerMap );
}
And I think I'd like to change it to use a scoped_array:

boost::scoped_array< WorkerThread > WorkerThreads;

WorkerThreads( new WorkerThread[/*...*/] )

Unfoortunately, the WorkerThread class does not have a default
constructor, and as such, the compiler does not allow me to cosntruct
a scoped_array. So maybe a scoped_array isn't the way to go, but it
seemed like most obvious choice. What would be an appropriate
solution?

I have no idea what 'scoped_array' is (it's not part of the Standard
Library, AFAICT), but can you tell me what's inaproppriate about, say,
'std::vector'?

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

I think that the main problem with vector will be the fact that he is
allocating those objects on the heap - they are pointers and vector is
not so great for those cases, in any case he will run in to the same
problem with vector since vector need the stored object to have default
ctor.
But why not to use boost::ptr_map? it was designed for holding pointers
which is what you code is doing. Then you don't need shared_ptr. Read
the docs for this.

[Marcus Kwok]

bo*******@yahoo.com wrote:

vector need the stored object to have default ctor.

Why do you say this?
#include <iostream>
#include <vector>

class NoDefaultConstructor {
public:
NoDefaultConstructor(int i) : i_(i) { }

private:
NoDefaultConstructor();
int i_;
};

int main()
{
std::vector<NoDefaultConstructor> v;
v.push_back(NoDefaultConstructor(42));
}

--
Marcus Kwok
Replace 'invalid' with 'net' to reply

[red floyd]

Marcus Kwok wrote:

bo*******@yahoo.com wrote:

vector need the stored object to have default ctor.

Why do you say this?
#include <iostream>
#include <vector>

class NoDefaultConstructor {
public:
NoDefaultConstructor(int i) : i_(i) { }

private:
NoDefaultConstructor();
int i_;
};

int main()
{
std::vector<NoDefaultConstructor> v;
v.push_back(NoDefaultConstructor(42));
}

Now add

v.resize(27);

after the push_back call.

[Victor Bazarov]

red floyd wrote:

Marcus Kwok wrote:

bo*******@yahoo.com wrote:

vector need the stored object to have default ctor.

Why do you say this?
#include <iostream>
#include <vector>

class NoDefaultConstructor {
public:
NoDefaultConstructor(int i) : i_(i) { }

private:
NoDefaultConstructor();
int i_;
};

int main()
{
std::vector<NoDefaultConstructor> v;
v.push_back(NoDefaultConstructor(42));
}

Now add

v.resize(27);

after the push_back call.

Well, duh. What if you don't? What if you limit yourself
to pushing/popping and accessing?

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[Marcus Kwok]

>> bo*******@yahoo.com wrote:

vector need the stored object to have default ctor.

Marcus Kwok wrote:

Why do you say this?

#include <iostream>
#include <vector>

class NoDefaultConstructor {
public:
NoDefaultConstructor(int i) : i_(i) { }

private:
NoDefaultConstructor();
int i_;
};

int main()
{
std::vector<NoDefaultConstructor> v;
v.push_back(NoDefaultConstructor(42));
}

red floyd <no*****@here.dude> wrote: Now add
v.resize(27);
after the push_back call.
Well of course that won't work, just like

NoDefaultConstructor ndc;

won't work.
Given the code from the original post:
WorkerThread *WorkerThreads[MAXTHREADS];

for ( int i=0; i<MAXTHREADS; i++ )
{
WorkerThreads[i] = new WorkerThread( TheHandlerMap );
}

Now using std::vector:

std::vector<WorkerThread*> WorkerThreads;
WorkerThreads.reserve(MAXTHREADS);

for (int i = 0; i < MAXTHREADS; ++i) {
WorkerThreads.push_back(new WorkerThread(TheHandlerMap));
}

--
Marcus Kwok
Replace 'invalid' with 'net' to reply

[Dennis Jones]

"Victor Bazarov" <v.********@comAcast.net> wrote in message
news:e5**********@news.datemas.de...

I have no idea what 'scoped_array' is (it's not part of the Standard
Library, AFAICT),
Surely you've heard of Boost? Many of its libraries are being considered
for inclusion in the standard.

but can you tell me what's inaproppriate about, say,
'std::vector'?

Actually, nothing...it's a perfectly acceptable solution. e.g.:

std::vector< boost::scoped_ptr<WorkerThread> > WorkerThreads;

WorkerThreads.reserve( cMaxThreads );
for ( int i=0; i<cMaxThreads; ++i )
{
WorkerThreads.push_back( boost::scoped_ptr<WorkerThread>( new
TWorkerThread( TheHandlerMap ) ) );
}

I can't initialize the array in the constructor's initializer list, but
initializing it with a loop in the constructor is only a minor inconvenience
compared to the benefit gained from the use of smart pointers.

Thanks for the 'vector' suggestion,

- Dennis

[Dennis Jones]

"Dennis Jones" <no****@nospam.com> wrote in message
news:CUNfg.11754$ho6.1518@trnddc07...

"Victor Bazarov" <v.********@comAcast.net> wrote in message
news:e5**********@news.datemas.de...

I have no idea what 'scoped_array' is (it's not part of the Standard
Library, AFAICT),

Surely you've heard of Boost? Many of its libraries are being considered
for inclusion in the standard.

but can you tell me what's inaproppriate about, say,
'std::vector'?

Actually, nothing...it's a perfectly acceptable solution. e.g.:

std::vector< boost::scoped_ptr<WorkerThread> > WorkerThreads;

Oops, that should have been 'boost::shared_ptr' (as scoped_ptr's won't
work).

- Dennis