reading a column from a text file

[slayer92]

Hi guys.Here is the part of code i use to read and store every value including spaces from a line


std::string line;
std::ifstream Host("Host.txt");
while (std::getline(Host, line))
{
double value;
std::istringstream iss(line);

while((value=iss.get()), iss)
{
save.push_back(value);
}
}

Im trying to make it work to read valuas from the first column of a text file including spaces and i cant get it done.
Right now all the values are on the first line and some of them are separated by spaces so save[0] is the first number from the first line,save[1] the second and so on.And im trying to make it work if i transpose all those values from first line to the first column.
Thanks

[Thomas1965]

How does the file look ?

[slayer92]

Well,if i open it with excel it has only column A with numbers on each row ,and sometimes there are empty cells on column A
1
2
"space"
1
3
etc
That is how i want it to be.When i made the program the values were like this:
1 2 "space" 1 3 on the first row and the program above worked with the second condiguration but not with the first configuration

[kbw]

How are columns separated? Is it spaces?

One way to read the values is to read each line, then pick out the numbers one at a time, these then form your columns.

For example, assuming whitespace separators and the double values that you used:

typedef std::vector<double> row_type;
typedef std::vector<row_type> grid_type;

row_type read_row(std::istream& is)
{
    row_type row;

    double value;
    while (is >> value)
        row.push_back(value);

    return std::move(row);
}

grid_type read_grid(std::istream& is)
{
    grid_type grid;

    std::string line;
    while (std::getline(is, line))
    {
        std::istringstream iss(line);
        row_type row = read_row(iss);
        grid.push_back(row);
    }

    return std::move(grid);
}

grid_type read_grid(std::string filename)
{
    std::ifstream feed(filename);
    return std::move(read_grid(feed));
}

You can pull out columns from that, or you can modify the example to read a specific column.

To pull out a column, you could do:

typedef row_type column_type;

column_type extract_column(const grid_type& grid, size_t col)
{
    if (grid.empty() || col >= grid[0].size())
        throw std::range_error("col too large");

    column_type column;
    column.resize(grid.size());
    for (const row_type& row : grid)
        column[idx++] = col < row.size() ? row[col] : NAN; // or 0.0

    return std::move(column);
}

[slayer92]

Thank you.But isnt there a simple solution i mean i only want to read and store every element only from column A and thats it, it doesnt matter what i do next with that vector of elements(btw my text file is basically an excel file but saved in a format.txt).and im supposed and im trying to make it with few lines of code

[Chervil]

isnt there a simple solution i mean i only want to read and store every element only from column A and thats it

Well, if this is the input file,

1
2
"space"
1
3
etc

then this should suffice:

#include <iostream>
#include <fstream>
#include <string>
#include <vector>

int main()
{
    std::vector<std::string> columnA;
    std::ifstream fin("Host.txt");
    
    for (std::string line; getline(fin, line);  )
        columnA.push_back(line);        
}

... or is there something I'm missing?