reading from a file

[suresh]

Hi,
I wrote a code like this and it failed to read from file. My question
what is the shortest code to read from a file and populate a vector?

vector<double> d;
ifstream in("myfile.txt");
copy(in.begin(),in.end(),back_inserter(d));

thanks
suresh

 

[Joshua Maurice]

Hi,
I wrote a code like this and it failed to read from file. My question
what is the shortest code to read from a file and  populate a vector?

vector<double> d;
ifstream in("myfile.txt");
copy(in.begin(),in.end(),back_inserter(d));

For starters, your code does not compile. Please see the FAQ on how to
post
http://www.parashift.com/c++-faq-lite/
Specifically please post complete compile-able examples. If you do not
know enough to post a complete compilable example, then do the closest
that you can. In the process of trying to make it compile (and work),
you might learn it on your own.

ifstream has no member functions begin and end.
http://cplusplus.com/reference/iostream/ifstream/

If you want to treat a std::istream as a readable sequence ala
iterators, see std::istream_iterator.
http://cplusplus.com/reference/std/iterator/istream_iterator/

A complete example would be:

#include <algorithm>
#include <fstream>
#include <functional>
#include <iterator>
#include <vector>

using namespace std;

int main()
{
vector<double> d;
ifstream in("myfile.txt");
copy(
istream_iterator<double>(in),
istream_iterator<double>(),
back_inserter(d)
);
}

Disclaimer: the code has only been tested to compile with
http://www.comeaucomputing.com/tryitout/
It has not been tested to produce correct results at runtime.

 

[suresh]

For starters, your code does not compile. Please see the FAQ on how to
posthttp://www.parashift.com/c++-faq-lite/
Specifically please post complete compile-able examples. If you do not
know enough to post a complete compilable example, then do the closest
that you can. In the process of trying to make it compile (and work),
you might learn it on your own.

ifstream has no member functions begin and end.http://cplusplus.com/reference/iostream/ifstream/

If you want to treat a std::istream as a readable sequence ala
iterators, see std::istream_iterator.http://cplusplus.com/reference/std/iterator/istream_iterator/

A complete example would be:

#include <algorithm>
#include <fstream>
#include <functional>
#include <iterator>
#include <vector>

using namespace std;

int main()
{
  vector<double> d;
  ifstream in("myfile.txt");
  copy(
    istream_iterator<double>(in),
    istream_iterator<double>(),
    back_inserter(d)
    );

}

Disclaimer: the code has only been tested to compile withhttp://www.comeaucomputing.com/tryitout/
It has not been tested to produce correct results at runtime.

thanks Joshua Maurice for the code. I wrote a non compiling code
because, I could not figure it out how to make it compile. I quickly
realised that there is no begin()/end() methods but then I was just
lost there. After using the copy algorithm for displaying contents of
containers on cout, I guessed that there must be a way to do the same
for input also. I tested your code and its working fine. thanks again
suresh

 

[James Kanze]

For starters, your code does not compile. Please see the FAQ on how to
posthttp://www.parashift.com/c++-faq-lite/
Specifically please post complete compile-able examples. If you do not
know enough to post a complete compilable example, then do the closest
that you can. In the process of trying to make it compile (and work),
you might learn it on your own.

ifstream has no member functions begin and
end.http://cplusplus.com/reference/iostream/ifstream/

If you want to treat a std::istream as a readable sequence ala
iterators, see std::istream_iterator.http://cplusplus.com/reference/std/iterator/istream_iterator/

A complete example would be:

#include <algorithm>
#include <fstream>
#include <functional>

You don't use this one.

#include <iterator>
#include <vector>

using namespace std;

int main()
{
vector<double> d;
ifstream in("myfile.txt");
copy(
istream_iterator<double>(in),
istream_iterator<double>(),
back_inserter(d)
);
}

You can do even better using the two iterator constructor of
vector:

std::istream in( "myfile.txt" );
std::vector<double> d(
(std::istream_iterator<double>( in )),
(std::istream_iterator<double>()));