ATL / WTL / STL

Re: Using STL input iterator reading from a file ??

4-Feb-03 0:21

Hi, everyone!

I meet with the following errors when compiling the
following simple codes. My IDE is VC 6.0.

Here are the codes.

--------
#include <iterator>
#include <fstream>
#include <iostream>

using namespace std;

void main()
{
ifstream ifile ("c:\\file1.txt");

istream_iterator<int, ptrdiff_t=""> r (ifile);
istream_iterator<int, ptrdiff_t=""> s (ifile);

}
--------

Here are the errors.

--------
Compiling...
testSTL.cpp
C:\PROGRAM FILES\MICROSOFT VISUAL STUDIO\MyProjects\testSTL\testSTL.cpp(11) : error C2664: '__thiscall std::istream_iterator<int,int,struct std::char_traits<int=""> >::std::istream_iterator<int,int,struct std::char_traits<int=""> >(class std::basic_istrea
m<int,struct std::char_traits<int=""> > &)' : cannot convert parameter 1 from 'class std::basic_ifstream<char,struct std::char_traits<char=""> >' to 'class std::basic_istream<int,struct std::char_traits<int=""> > &'
A reference that is not to 'const' cannot be bound to a non-lvalue
C:\PROGRAM FILES\MICROSOFT VISUAL STUDIO\MyProjects\testSTL\testSTL.cpp(12) : error C2664: '__thiscall std::istream_iterator<int,int,struct std::char_traits<int=""> >::std::istream_iterator<int,int,struct std::char_traits<int=""> >(class std::basic_istrea
m<int,struct std::char_traits<int=""> > &)' : cannot convert parameter 1 from 'class std::basic_ifstream<char,struct std::char_traits<char=""> >' to 'class std::basic_istream<int,struct std::char_traits<int=""> > &'
A reference that is not to 'const' cannot be bound to a non-lvalue
Error executing cl.exe.

testSTL.obj - 2 error(s), 0 warning(s)
--------

How to resolve the trouble?

Thanks in advance,
George

Joaquín M López Muñoz4-Feb-03 1:40

Re: Using STL input iterator reading from a file ??

4-Feb-03 1:40

Next time, check the "Display this message as-is (no HTML)" ooption so that the < and > characters will appear.

You're supplying nonsensical parameters to istream_iterator. Replace with:

istream_iterator<int> r (ifile);

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

George24-Feb-03 1:47

Re: Using STL input iterator reading from a file ??

4-Feb-03 1:47

Thanks, Joaquín buddies!

I have seen several times the istream_iterator
is initialized with the ptrdiff_t parameter.

But why I can not use it here?

Cheers,
George

Joaquín M López Muñoz4-Feb-03 1:50

Re: Using STL input iterator reading from a file ??

4-Feb-03 1:50

The standard set of parameters of istream_iterator is

template <
  class T,
  class charT = char,
  class traits = char_traits<charT>,
  class Distance = ptrdiff_t
> istream_iterator;

So the ptrdiff_t parameter, if anywhere, should be in the fourth position. (Beware, VC++ 6.0 is non-standard in this respect and expects a maximum of three parameters.)

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

George24-Feb-03 2:12

Re: Using STL input iterator reading from a file ??

4-Feb-03 2:12

Hi, Joaquín buddies!

I find out the definitions in VC6.0.

--------
template<class U, class E = char, class T = char_traits<E> >
class istream_iterator
: public iterator<input_iterator_tag, U, ptrdiff_t>
--------

So, if I want to use the parameter ptrdiff_t and read int from a file, how could I assign parameter? <int, ??, ptrdiff_t>? What should be the second parameter?

Thanks in advance,
George

Joaquín M López Muñoz4-Feb-03 2:15

Re: Using STL input iterator reading from a file ??

4-Feb-03 2:15

So, if I want to use the parameter ptrdiff_t and read int from a file, how could I assign parameter?

What do you want to specify ptrdiff_t for?

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

George24-Feb-03 2:33

Re: Using STL input iterator reading from a file ??

4-Feb-03 2:33

Hi, Joaquín pal!

To tell the truth, I myself do not
understand why I should use ptrdiff_t.
I use it simply because I am reading
some codes of a project which is developed
from BC IDE and all the pieces of codes
uses the keyword.

Can you show me how to use ptrdiff_t
in my scenario?

Thanks in advance,
George

Joaquín M López Muñoz4-Feb-03 4:22

Re: Using STL input iterator reading from a file ??

4-Feb-03 4:22

Ignore it; just use istream_iterator<int>. If you want to know more about the additional parameters of istream_iterator read some C++ reference, but usually you won't need them anyway.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

George24-Feb-03 6:05

Question about STL output iterator.

4-Feb-03 6:05

Thanks, Joaquín buddies!

I will follow your advice. Smile | :)

Cheers,
George

George23-Feb-03 22:24

3-Feb-03 22:24

Hi, everyone!

My STL tutorial says,

--------
Assignment through the same value of the iterator should happen only once.

ostream_iterator<int> r (cout);
*r = 0;
*r = 1;

is not a valid code sequence.
--------

But I tried the above code sample, it works OK!
The output is 0 and 1.

What is the meaning of the tutorial?

Thanks in advance,
George

Joaquín M López Muñoz3-Feb-03 23:02

3-Feb-03 23:02

You've hit undefined behavior. If VC++'s STL implementation happens to work this way, this is only sheer luck, and as you know good luck is something you'd better not count on Smile | :)

So, I suggest you stick to the standard and write:

...
*r++ = 0;
*r++ = 1;

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

George24-Feb-03 0:11

4-Feb-03 0:11

Hi, Joaquín pal!

I am a newbie of STL. I do not understand
what is your meaning clearly. What means
"undefined behavior"? Can you give me a more
clarified and detailed description of my case?

Thanks in advance,
George

Joaquín M López Muñoz4-Feb-03 1:29

4-Feb-03 1:29

Undefined behavior means you're not doing things as required and the compiler can do anything it wishes (refusing to compile, show different behaviors in debug/release mode, crash in run-time, etc.)
The rule for output iterators is that you cannot assign a value to an interator more than once without incrementing between wrtie operations.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

George24-Feb-03 1:44

4-Feb-03 1:44

Thanks, Joaquín buddies!

George

George24-Feb-03 0:49

Meeting troubles when compiling simple STL program.

4-Feb-03 0:49

Hi, Joaquín buddies!

I have tried your codes. It works OK!
But I still do not understand what is the
theory of output iterator, like the following,

--------
Assignment through the same value of the
iterator should happen only once.
--------

I think my code must have some potential error as you
mentioned. But I do not know what the error is.

Can you explain it to me?

Thanks in advance,
George

George23-Feb-03 17:35

Re: Meeting troubles when compiling simple STL program.

3-Feb-03 17:35

Hi, everyone!

I meet with the following trouble when compiling the
following simple STL program.

The error message is, ostream_iterator undeclared.
My IDE is VC 6.0.

Here are the source codes,

--------
#include "iterator"
#include "iostream"

void main()
{
ostream_iterator<int> r (cout);
*r = 0;
}
--------

Thanks in advance,
George

Michael Dunn3-Feb-03 19:56

Michael Dunn

3-Feb-03 19:56

See 2.1 I'm trying to use a standard C++ library class (like cout, cin, or string) but the compiler gives an undeclared identifier error (C2065) on those names. Why?[^]

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Re: Meeting troubles when compiling simple STL program.

George23-Feb-03 22:21

Re: Meeting troubles when compiling simple STL program.

3-Feb-03 22:21

Thanks, Michael buddies!

George

Ben Burnett3-Feb-03 20:10

Ben Burnett

3-Feb-03 20:10

ostream_iterator is in the std namespace [^]. In short, a namespace is a scope of which contains one or more related functions/classes/structs. To use members of a namespace you either have to 'import' them (with the nasty using namespace std;--nasty because it pollutes the global scope...read the tutorial for more information) or explicitly prefix each one you use with the namespace's name.

The following should do what you want:

#include <iterator>
#include <iostream>

int main () {
	std::ostream_iterator<int> r ( std::cout );
	*r = 0;
}

My suggestion is that you read up on the STLs. There are many great books on the subject, as well as some excellent articles on this site.

cheers,
-B

Re: Meeting troubles when compiling simple STL program.

George23-Feb-03 22:17