Re: [Boost-users] Problem with list_of, make_shared and shared_ptr

Subject: Re: [Boost-users] Problem with list_of, make_shared and shared_ptr
From: OvermindDL1 (overminddl1_at_[hidden])
Date: 2010-07-24 15:56:45

On Fri, Jul 23, 2010 at 8:06 AM, alapex0310_at_[hidden]
<alapex0310_at_[hidden]> wrote:
> Hi,
>
> I am using boost::list_of to pass a vector of pairs of string + "unsigned
> char" to SomeClass (as it can be seen in the typedef below - keys_t). This
> passes the whole vector to SomeClass which copies the vector in the keys_
> private variable. The problem is: the copy ctor now copies the full vector
> in each SomeClass. To prevent this, as you can see, I have defined another
> data member which is a reference to const keys_t in my class and am
> initializing it in the member initialization list of the constructor with
> the value of keys_ and having the copy constructor copy just the reference
> of keys_ (rkeys_, that is - as you can see in the member initialization list
> of the copy ctor) instead of the full vector but the new SomeClass then
> holds an uninitialized vector (keys_) which is ugly and I hate seeing it in
> the class. Can I possible use Boost::make_shared with boost::list_of to
> return me a pointer to whatever (vector of type keys_t) boost::list_of
> returns and store that pointer instead in my class (e.g. keys_t typedef then
> reflects boost::shared_ptr instead of a traditional pointer) Â instead of the
> full vector. Specifying the arbitrary constants (apparently using
> boost::list_of) right in the constructor call is a requirement. Is there any
> way I can do it? Of course, I guess I could use boost::make_shared to return
> me a boost::shared_ptr to keys_t but my code is not even compiling and
> giving me errors in boost headers:
>
>
> std::vector<std::pair<std::string,unsigned char>> keys_t;
>
> class SomeClass
> {
> public:
> Â  Â SomeClass(std::string nameStr, keys_t keys) : keys_(keys),
>
> Â rkeys_(keys_) {}
> Â  Â SomeClass(const SomeClass &koa) : rkeys_(koa.keys_) Â  Â  Â {}
>
> private:
>             keys_t    keys_;
> Â  Â const keys_t &rkeys_;
>
> };
>
> SomeClass *psc = new SomeClass( Â  Â "MyClass", list_of<pair<string,unsigned
> char>>
> Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â ("one", Â  Â  Â  Â 1)
> Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â ("two", Â  Â  Â  Â 2)
> Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â ("three", Â  Â 3)
> Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â ("four", Â  Â 4)
> Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â ("five", Â  Â 5)
> Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â ("six", Â  Â  Â  Â 6));
>
> I read in boost::doc that I cannot pass shared_ptr directly as a function
> argument because of temporary problems. So, I cannot pass a shared_ptr to
> the constructor of SomeClass and that's the primary reason I hope if you can
> help me use make_shared or something similar to get the job done. The
> constraint is: I *must* pass the arbitrary number of pairs of
> string-unsigned-char in my constructor and that's why I am using list_of.
> Any way out?

it only means you cannot do this:
  funcCall(shared_ptr<mytype>(new mytype));
Instead you should do this:
  shared_ptr<mytype> mytypePtr(new mytype);
  funcCall(mytypePtr);