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kak3012
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 Posted: Thu Feb 24, 2005 9:13 pm Post subject: read line |
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Hi,
I have a text file I will read it and write out binary. The file includes
256 coloums.
I use
while (infile.good())
{
infile.getline (buffer,2200);
cout<
exit(0);
}
so I can see the file.
Each field is seperated by 1 TAB or 2 TABS I mean t.
Is there a way to read this file at once into an array, line by line. They
are all numbers.
Regards...
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saper
Guest
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| Posted: Fri Feb 25, 2005 8:11 am Post subject: Re: read line |
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long double ld=50;
printf("%Lg",ld);
and display show -6.8065E+038
no 50
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Jerry Coffin
Guest
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| Posted: Fri Feb 25, 2005 4:28 pm Post subject: Re: read line |
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kak3012 wrote:
| Quote: | Hi,
I have a text file I will read it and write out binary. The file
includes
256 coloums.
I use
while (infile.good())
{
infile.getline (buffer,2200);
cout<
exit(0);
}
so I can see the file.
Each field is seperated by 1 TAB or 2 TABS I mean t.
Is there a way to read this file at once into an array, line by line.
They
are all numbers.
|
It's not entirely clear whether you want an array of numbers, or an
array of strings, each representing a single line from the file. For
an array (or technically, a vector, but you rarely want an array
anyway) of numbers, you could do something like this:
typedef double type; // use type appropriate to your numbers.
std::vector
std::copy(std::istream_iterator<type>(infile),
std::istream_iterator<type>(),
std::back_inserter(numbers));
If you want the numbers kept as strings, but still want each as an item
in the vector, you can just change 'type' from 'double' to
'std::string'.
Oddly enough, if you want each LINE as a string in an array, it's a
little more difficult (though not much). You can do it a little like
above by creating a class that acts like a string, except that
operator>> reads a whole line instead of a single token. It's usually
easier, however, to do the job explicitly, with something like:
std::vector<std::string> numbers;
std::string temp;
while(infile.good()) {
std::getline(infile, temp);
numbers.push_back(temp);
}
A few notes about C++ in general: as mentioned above, especially to
start with, you probably won't encounter many reasons to use arrays --
you'll usually want to use vectors instead (or std::string instead of
arrays of char). Going along with that, you rarely want to use
istream::getline -- you'll almost always want to use std::getline
instead, because you'll be reading into a string instead of an array of
char. The first bit of code I have above probably looks rather foreign
to you right now, since you've probably never seen or used those parts
of the standard library yet -- but studying them is an effort that will
be well worthwhile, at least IMO. You can certainly read doubles (for
example) into a vector with code much like the second piece above --
but I think it's worth the work to learn how to do it the first way
I've given above instead.
--
Later,
Jerry.
The universe is a figment of its own imagination.
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