Hello, I did it before... But I forgot. I have a file with some data:
0.5 0.6 0.7 1.2 1.5
How can I read this in c++? I did it with stream... something like:
float var = 0;
stream >> var;
views:
264answers:
5
A:
Something like this. The << operator treats spaces as a separator.
float array[5] = {0.0f};
for(int i = 0; i < 5; i++)
{
stream >> array[i];
}
BTW I did 5 since you had 5 in your example. (and I am assuming you have the stream setup)
Ólafur Waage
2009-11-02 09:49:12
@Ólafur - how is that going to work? Perhaps my C++ syntax memory is waay off, but as I read it, you're going to read from the file into the *address* of `var`, not into the next position in the array. You should want to put the `[i]` back at the end of `var`, as I had modified for you earlier - unless this is a way of using arrays I've just never seen or heard of before.
warren
2009-11-02 12:53:34
Ya just an error from me.
Ólafur Waage
2009-11-02 13:08:03
A:
Do you mean how to open a file and read data from it?
That should look something like this:
float var;
ifstream infile("filename");
if(infile.good()){
while(!infile.eof()){
infile >> var;
cout << var << "is the next value\n";
}
}
warren
2009-11-02 09:49:47
this is how I've always done file I/O; and how I've always seen it in various reference materials.
warren
2009-11-02 12:55:16
warren, your code is incorrect, see my comment at Vijay's answer (I didn't downvote, though).
avakar
2009-11-02 13:27:01
eof doesn't return true until after the first failed attempt to read from the file. So (unless the file ends immediately after the last number, without a newline) your loop will perform an extra iteration.
Thomas Padron-McCarthy
2009-11-02 13:45:37
Actually, avakar's "bumped into the end of file during the last extraction" is a better explanation than my "first failed attempt to read". If the file ends immediately after the last number, eof will turn true after the last ">>" operation that was successfull. Yes, on a lower level there was a byte-read that failed involved, but the ">>" operation was successful in that case, so "bumped into" is much better pedagogically.
Thomas Padron-McCarthy
2009-11-02 14:02:07
@avakar - don't see an answer from Vijay. @Thomas - that's what the `.good()` call is supposed to do, I thought - make sure the file is healthy before continuing? I don't mind being wrong, but I'm a little concerned that this is how every reference manual and teacher I've ever seen has done it, and how I've been doing it for ~15 years, and it's not right :-\
warren
2009-11-02 14:20:00
The other answer was deleted. The call to good just checks that the file could be opened, and doesn't help for the problem with the loop. And yes, this is a horribly common error. (So don't delete your answer, you too! It, and the discussion, is needed as a warning.)
Thomas Padron-McCarthy
2009-11-02 17:11:13
+3
A:
Something like this?
std::ifstream stream("C:/a.txt");
float var = 0;
while(stream >> var)
{
//Do some processing
}
Naveen
2009-11-02 09:49:54
+3
A:
The following snippet should give you a clue. Don't forget to include <fstream>.
std::ifstream fin("filename.txt");
float value;
while (fin >> value)
{
// Do whatever you want with the value
}
Do not try to test fin.eof() it won't tell you if you're about to bump to the end of file.
avakar
2009-11-02 09:51:06