Assigning a portion of a getline to a variable

What is a good way to read a text file and read each line, then assign
data to variables? I have this so far,

#include <iostream>
#include <fstream>

using namespace std;

string BATCHNUMBER;
string BIS ="100";
string DEPARTMENT = "04";
string DESCRIPTION;
string DOCUMENTDATE;
string DOCUMENT;
string DUEDATE;
string FUND = "31Y";
string SCREEN = "31";

void main()
{
ifstream OpenFile;
OpenFile.open("youth.txt");
if(!OpenFile)
{
cout << "Error opening file! Aborting..." << endl;
exit(1);
}
else
cout << "File successfully opened..." << endl << endl;

cout << "Batch Number: ";
cin >> BATCHNUMBER;
cout << "Description: ";
cin >> DESCRIPTION;
cout << "Document Date: ";
cin >> DOCUMENTDATE;
cout << "Document: ";
cin >> DOCUMENT;
cout << "Due Date: ";
cin >> DUEDATE;

char line[50];
string vender[7];

while(!OpenFile.eof())
{
OpenFile.getline(line,50);
cout << line << endl;
}
OpenFile.close();
}

For example, if I want positions 1-7 to be assigned to a string
vender, then positions 10-12 to be assigned to a different string how
is that accomplished?

Here is a sample of the data file:

Y0TH004 210 100 50 5
Y0TH005 220 25 10 5
Y0TH008 200 50 60 55 1000

I have tested this and can read the file. After I get everything
loaded into variables, I will have to output to some other file to
format the data the way that is needed for an import to another
application.

Thanks for you help in advance.

re: Assigning a portion of a getline to a variable

"Michael Easterly" <measterly@mchsi.com> wrote in message
news:5484cc9f.0405281020.6ac58319@posting.google.c om...[color=blue]
> What is a good way to read a text file and read each line, then assign
> data to variables? I have this so far,
>
> #include <iostream>
> #include <fstream>
>
> using namespace std;
>
> string BATCHNUMBER;
> string BIS ="100";
> string DEPARTMENT = "04";
> string DESCRIPTION;
> string DOCUMENTDATE;
> string DOCUMENT;
> string DUEDATE;
> string FUND = "31Y";
> string SCREEN = "31";[/color]

Convention is to only use all upper case identifiers
for macros.
[color=blue]
>
> void main()[/color]

int main()
[color=blue]
> {
> ifstream OpenFile;
> OpenFile.open("youth.txt");
> if(!OpenFile)
> {
> cout << "Error opening file! Aborting..." << endl;
> exit(1);[/color]

IMO better would be:

return EXIT_FAILURE; /* needs #incluce <cstdlib> */
[color=blue]
> }
> else
> cout << "File successfully opened..." << endl << endl;
>
> cout << "Batch Number: ";
> cin >> BATCHNUMBER;
> cout << "Description: ";
> cin >> DESCRIPTION;
> cout << "Document Date: ";
> cin >> DOCUMENTDATE;
> cout << "Document: ";
> cin >> DOCUMENT;
> cout << "Due Date: ";
> cin >> DUEDATE;
>
> char line[50];
> string vender[7];
>
> while(!OpenFile.eof())[/color]

eof() does not return true until *after* a failed read attempt.
[color=blue]
> {
> OpenFile.getline(line,50);
> cout << line << endl;
> }
> OpenFile.close();[/color]

The ifstream destructor will automatically close the
file for you. This statement is redundant (but harmless).
[color=blue]
> }
>
> For example, if I want positions 1-7 to be assigned to a string
> vender, then positions 10-12 to be assigned to a different string how
> is that accomplished?
>
> Here is a sample of the data file:
>
> Y0TH004 210 100 50 5
> Y0TH005 220 25 10 5
> Y0TH008 200 50 60 55 1000[/color]

You can address specific positions in a std::string with its
[] operator, and you can get subsequences out of a std::string
with its 'substr()' member functions. BUT:
Your data does not appear to be column-aligned, but simply
separated by whitespace. So extracting particular columns
won't work.
[color=blue]
>
> I have tested this and can read the file. After I get everything
> loaded into variables, I will have to output to some other file to
> format the data the way that is needed for an import to another
> application.
>
> Thanks for you help in advance.[/color]

The following extracts each line as a 'record', stores each
whitespace-separated string into a 'field' of each record,
and outputs the data to cout (separating 'fields' with spaces,
and 'records' with newlines:


#include <cstdlib>
#include <fstream>
#include <iostream>
#include <istream>
#include <ostream>
#include <sstream>
#include <string>

class Record
{
std::string line;
std::string batchnumber;
std::string description;
std::string documentdate;
std::string document;
std::string duedate;

friend std::istream& operator>>(std::istream& is, Record& r)
{
return is >> r.line[color=blue][color=green]
>> r.batchnumber
>> r.description
>> r.documentdate
>> r.document
>> r.duedate;[/color][/color]
}

friend std::ostream& operator<<(std::ostream& os, const Record& r)
{
return os << r.line << ' '
<< r.batchnumber << ' '
<< r.description << ' '
<< r.documentdate << ' '
<< r.document << ' '
<< r.duedate;
}
};

const int status[] = {EXIT_SUCCESS, EXIT_FAILURE};

int main()
{
std::string filename("data.txt");
std::ifstream input(filename.c_str());
bool err(!input);

if(!err)
{
std::string line;

while(std::getline(input, line))
{
std::istringstream iss(line);
Record rec;
iss >> rec;
std::cout << rec << '\n';
}

if(err = (!input && !input.eof()))
cerr << "Error reading file '" << filename << "'\n";
}
else
cerr << "Cannot open file '" << filename << "'\n";

return status[err];
}

-Mike

re: Assigning a portion of a getline to a variable

On 28 May 2004 11:20:27 -0700 in comp.lang.c++, measterly@mchsi.com
(Michael Easterly) wrote,[color=blue]
>What is a good way to read a text file and read each line, then assign
>data to variables?[/color]

There is no single answer to that, it depends on many things such as how
complex your data format is, and what kind of error recovery you
require. But,
[color=blue]
> while(!OpenFile.eof())
> {[/color]

that isn't part of it. Don't loop on eof(), instead read until reading
fails. Then check eof() to see if that was the reason, if you still
care.

std::string line;
while(std::getline(openfile, line)
{
[color=blue]
>For example, if I want positions 1-7 to be assigned to a string
>vender, then positions 10-12 to be assigned to a different string how
>is that accomplished?
>
>Here is a sample of the data file:
>
>Y0TH004 210 100 50 5[/color]

OK, your fields appear to be delimited by whitespace. That makes things
easy, since that's the default behavior for stream formatting
operator>>(). You could do something like:

while(std::getline(openfile, line)
{
std::istringstream parse(line);
parse >> f1 >> f2 >> f3 >> f4;
if(parse.good())
// do something with the data.
}

For more complicated input format, one of the first things I think of
these days is the regex library from http://www.boost.org