STL: Could you make this snippet more efficient

[pedagani]

Dear comp.lang.c++,

Could you make this snippet more efficient? As you see I have too many
variables introduced in the code.

//Read set of integers from a file on line by line basis in a STL set
//fp is pre-defined
for(;!fp.eof(); )
{
string linestr;
getline(fp,line str);
istringstream strstreamline(l inestr);
istream_iterato r<unsigned intintstream(st rstreamline);
set<unsigned intpckset;
copy ( intstream , istream_iterato r<unsigned int>() ,
inserter(modpck set,modpckset.b egin ( ) ));
}

Thanks in advance.

[pedagani]

On Dec 3, 3:23 pm, "Daniel T." <danie...@earth link.netwrote:

pedag...@gmail. com wrote:

Could you make this snippet more efficient? As you see I have too many
variables introduced in the code.

//Read set of integers from a file on line by line basis in a STL set
//fp is pre-defined
for(;!fp.eof(); )
{
string linestr;
getline(fp,line str);
istringstream strstreamline(l inestr);
istream_iterato r<unsigned intintstream(st rstreamline);
set<unsigned intpckset;
copy ( intstream , istream_iterato r<unsigned int>() ,
inserter(modpck set,modpckset.b egin ( ) ));
}

Thanks in advance.

First let's clean up the code you have.

set< unsigned int modpckset; // has to be defined outside the loop
string line;
while ( getline( fp, line ) ) // proper way to read until end of file
{
istringstream ss( line );
copy( istream_iterato r< unsigned int >( ss ),
istream_iterato r< unsigned int >(),
inserter( modpckset, modpckset.begin () ) );

}

With the above code, getline will read in a line of the file at a time,
then parse it out to a bunch of unsigned ints. We don't need to do the
extra step:

set< unsigned int modpckset;
copy( istream_iterato r< unsigned int >( fp ),
istream_iterato r< unsigned int >(),
inserter( modpckset, modpckset.begin () ) );

The above will do the same thing.

Now, if your goal was to read each line into a separate set, say you
want to end up with a vector of sets, then you would need to read each
line separately.

vector< set< unsigned int all_sets;
string line;
while ( getline( fp, line ) )
{
istringstream ss( line );
all_sets.push_b ack( set< unsigned int >() );
copy( istream_iterato r< unsigned int >( ss ),
istream_iterato r< unsigned int >(),
inserter( all_sets.back() , all_sets.back() .begin() ) );
}

Very nice. If its not too much clutter one could do the same as

set< unsigned int modpckset; // has to be defined outside the loop
string line;
while ( getline( fp, line ) ) // proper way to read until end of file
{
copy( istream_iterato r< unsigned int >( istringstream (line) ),
istream_iterato r< unsigned int >(),
inserter( modpckset, modpckset.begin () ) );
//...
}

[Victor Bazarov]

Daniel T. wrote:

[..]
set< unsigned int modpckset; // has to be defined outside the loop
string line;
while ( getline( fp, line ) ) // proper way to read until end of file
{
istringstream ss( line );
copy( istream_iterato r< unsigned int >( ss ),
istream_iterato r< unsigned int >(),
inserter( modpckset, modpckset.begin () ) );
}

With the above code, getline will read in a line of the file at a
time, then parse it out to a bunch of unsigned ints. We don't need to
do the extra step:

set< unsigned int modpckset;
copy( istream_iterato r< unsigned int >( fp ),
istream_iterato r< unsigned int >(),
inserter( modpckset, modpckset.begin () ) );

The above will do the same thing.

Really? Will it? What if it can't copy (there is 'O' instead of '0'
somewhere in the file)? Will it attempt to read again from the next
line?

[..]

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

[Daniel T.]

"Victor Bazarov" <v.********@com Acast.netwrote:

Daniel T. wrote:

[..]
set< unsigned int modpckset; // has to be defined outside the loop
string line;
while ( getline( fp, line ) ) // proper way to read until end of file
{
istringstream ss( line );
copy( istream_iterato r< unsigned int >( ss ),
istream_iterato r< unsigned int >(),
inserter( modpckset, modpckset.begin () ) );
}

With the above code, getline will read in a line of the file at a
time, then parse it out to a bunch of unsigned ints. We don't need to
do the extra step:

set< unsigned int modpckset;
copy( istream_iterato r< unsigned int >( fp ),
istream_iterato r< unsigned int >(),
inserter( modpckset, modpckset.begin () ) );

The above will do the same thing.

Really? Will it? What if it can't copy (there is 'O' instead of '0'
somewhere in the file)? Will it attempt to read again from the next
line?

Sorry, at some point while writing the post, I had written that I was
assuming that the file contained all unsigned ints. I must have
accidentally cut that line out.