std::string problems.

I can't seem to get get working with strings. Why can't I use infile.get(row, columns);?

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

int main(int argc, char** argv)
{
    std::ifstream infile("test.txt");
    int columns, ctrl;
    std::string row;
    std::vector <std::string> matrix;
    infile >> columns;
    infile.get();
    for (int i = 0; i < columns; i++)
        infile.get(row[i]);
    matrix.push_back(row);
    for (int index = 1; !infile.eof(); index++)
    {
        ctrl = !(index%2)*(columns-1);
        for (int i = 0; i < columns; i++)
            infile.get(row[ctrl-i]);
        matrix.push_back(row);
    }
    infile.close();
    for (int j = 0; j < columns; j++)
        for (int i = 0; i < matrix.size(); i++)
            std::cout << matrix[i][j];
    std::cin.get();
    return 0;
}

........        CCCCCCCCmmmmmmmmdddddddd

test.txt contains:
5
A uoChdsWvee earrtl acoutis ondmC .

One more unrelated question. At first I accidentally forgot to #include<string>, but my program still compliled. Why?

ne555 (10692)

infile.get(row[i]); You never reserve the space in your string. row.resize( columns );
edit: note that it is resize, no reserve, or you could corrupt the container.

Aharti..  eeuu  uu  ooCCooeeccmmCCeeaadd

what it should be?

I guess that some header does include at string.

Last edited on

ne555 (10692)

 ctrl = !(index%2)*(columns-1); //ctrl=0 or ctrl=column-1
//ctrl = (index%2) ? 0 : columns-1;
//...
infile.get( row[ctrl-i] ); //if ctrl=0 -> out_of_range

Last edited on

Browni3141 (578)

Thanks, for some reason I thought string memory was automatically allocated when you add to the string. I had a lot of other mistakes but they're fixed now.

I still need to know if there is a way to use infile.get() to extract a specific amount of characters and store them in a std::string.

filipe (1165)

Thanks, for some reason I thought string memory was automatically allocated when you add to the string.

And it is. But you were trying to access an out of bounds subscript. If you just did this:

1
2
3

char ch;
infile.get(ch);
row += ch;

it would have been fine.

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