help regarding syntax

[Giuseppe:G:]

Hi, any idea on what is this code doing:

//=================================
1 #include <boost/scoped_ptr.hpp>

....

3 typedef std::vector<std::vector<pair<size_t, size_t> > > ParamsType;

5 /*
6 *Is the following a boost shared pointer to a "ParamsType" object?
7 */
8 shared_ptr<ParamsType>& params;

....
14 params.reset(new ParamsType(m_pred_map->size()));
15 for (size_t pid = 0; pid < m_pred_map->size(); ++pid) {
16 vector<pair<size_t, size_t> >& param = (*params)[pid]; // ??
...
}
//=================================

I have problems with lines 14 & 16. First of all, is ParamsType a vector
of vectors of pairs? Then I think params is a pointer to that. Then, we
probably instantiate a new ParamsType and let params point at it. Right?

But then, what's happening in line 16?


Thanks in advance

Giuseppe

 

[Giuseppe:G:]

Anybody? please.. Is

vector<pair<size_t, size_t> >& param = (*params)[pid];

a kind of cast?

cheers
Giuseppe

 

[joseph cook]

Anybody? please.. Is

vector<pair<size_t, size_t> >& param = (*params)[pid];

a kind of cast?

cheers
Giuseppe

Hi, any idea on what is this code doing:

//=================================
1 #include <boost/scoped_ptr.hpp>

3 typedef std::vector<std::vector<pair<size_t, size_t> > > ParamsType;

5 /*
6 *Is the following a boost shared pointer to a "ParamsType" object?
7 */
8 shared_ptr<ParamsType>& params;

...
14 params.reset(new ParamsType(m_pred_map->size()));
15 for (size_t pid = 0; pid < m_pred_map->size(); ++pid) {
16       vector<pair<size_t, size_t> >& param = (*params)[pid]; // ??
    ...
}
//=================================

I have problems with lines 14 & 16. First of all, is ParamsType a vector
of vectors of pairs? Then I think params is a pointer to that. Then, we
probably instantiate a new ParamsType and let params point at it. Right?

But then, what's happening in line 16?

If you think of it as a 2D matrix of "pair" objects, then this loop is
getting each "row" of of the matrix. The term "param" in most cases
would be used as a reference, because it is easier to read/type than
repeating "(*params)[pid]" everywhere else in the loop. It is just an
alias.

hth,
Joe Cook

 

[Giuseppe:G:]

Thanks Joe! Now I get it. It's as if we're "isolating" single rows ( or
columns) and then managing them through param.

Regards
Giuseppe