Re: input formatted file

From:
"Jim Langston" <tazmaster@rocketmail.com>
Newsgroups:
comp.lang.c++
Date:
Sat, 24 Nov 2007 12:52:56 -0800
Message-ID:
<Qa02j.42$DB7.41@newsfe05.lga>
"James Kanze" <james.kanze@gmail.com> wrote in message
news:fb7ae73a-a05f-45b3-bd54-421528186843@j20g2000hsi.googlegroups.com...
On Nov 24, 5:37 pm, "Jim Langston" <tazmas...@rocketmail.com> wrote:

"Jun" <junh...@gmail.com> wrote in message

news:81126096-6872-439f-9bbc-0ebd631536a2@y5g2000hsf.googlegroups.com...

I've a data file

========
4 1 1 1 1
5 1 1 1 1 1
2 1 1
========

first column represents the how many values in this line, and then
followed by values. I've seen some codes using

*******************************
ifstream inf

while(inf >> data1 >> data2)
*******************************
to read data, just very beautiful and simple code, could anyone give
me some advices for my case? thank you in advance.


One thing I would do is use std::getline( inf, somestring );
then put it into a stringstream.


Why a stringstream, and not an istringstream? You don't want to
write to it?

----------

I don't use streams that often other than stringstream where I do tend to do
both input and output and the full blown stringstream is required. I'm not
100% sure of the advantages of using istringstream over stringstream though,
other than maybe some overhead costs.

std::stringstream Data( somestring );
At this point you can check if the number of values are correct.

int Count;
if ( Data >> Count )
{
   int Value;
   int ValueCount;
   while ( Data >> Value )
   {
      ValueCount++;
      // dosomething with Value
   }
   if ( ValueCount != Count )
  {
      // throw error here. Number at beginning does not match
     // number of values.
  }
}


Even easier:

    std::istringstream s( line ) ;
    size_t count ;
    s >> count ;
    std::vector< int > data((std::istream_iterator< int >( s )),
                             (std::istream_iterator< int >()) ) ;
    if ( ! s ) {
        // Some input error...
    } else if ( data.size() != count ) {
        // syntax error
    }

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