C++ read from istream until newline (but not whitespace)

Question

I have a std::istream which refers to matrix data, something like:

0.0 1.0 2.0
3.0 4.0 5.0

Now, in order to assess the number of columns I would like to have some code like:

std::vector<double> vec;
double x;
while( (...something...) && (istream >> x) )
{
    vec.push_back(x); 
}
//Here vec should contain 0.0, 1.0 and 2.0

where the ...something... part evaluates to false after I read 2.0 and istream at the point should be at 3.0 so that the next

istream >> x;

should set x equal to 3.0.

How would you achieve this result? I guess that the while condition

Thank you very much in advance for your help!

Answer 1

Read the lines into a std::string using std::string::getline(), then assign the string to a std::istringstream object, and extract the data from that rather than directly from istream.

Answer 2

Read the number, then read one character to see if it's newline.

Answer 3

You can use std::istream::peek() to check if the next character is a newline. See this entry in the cplusplus.com reference.

Answer 4

Use the peek method to check the next character:

while ((istream.peek()!='\n') && (istream>>x))

Answer 5

std::vector<double> vec;
{
   std::string line;
   std::getline( ifile, line );
   std::istringstream is(line);
   std::copy( std::istream_iterator<double>(is), std::istream_iterator<double>(),
              std::back_inserter(vec) );
}
std::cout << "Input has " << vec.size() << " columns." << std::endl;
std::cout << "Read values are: ";
std::copy( vec.begin(), vec.end(), 
           std::ostream_iterator<double>( std::cout, " " ) );
std::cout << std::endl;