istream_iterator and ostream_iterator learning experience

Reprinted from fdl19881

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istream_iterator defined <iterator> header file

Istream_iterator way to define variables

istream_iterator <T> in (strm); (wherein T indicates istream_iterator this type of input, strm stream is directed istream_iterator)

Providing the operator input (>>) and any type of output operators (<<) can create objects and ostream_iteratorcfq istream_iterator objects, i.e. their class overrides these two functions:

istream &operator >> (istream &is, &MyClass c);

和 ostream &operator << (ostream &os , const  &MyClass c);

1. If strm is empty, i.e. such istream <T> in (); while, in this case the variable is equivalent to the EOF flag is directed the iterator

Figure defined as follows: (eoff below that I deliberately wrote, just to let everyone know just from the name will do)

istream_iterator<T> eoff ;
  
  

Eoff private variables found in _Myistr is 0x000000000;

Then look at a definition: (Note: the contents of test.txt is 10 (EOF))

  
  
ifstream infile("f:\\test.txt");
istream_iterator< int> input(infile);
  
  

Check again when vs2008 debugging:

We find no: private member _Myistr input variable is not zero up! And private members _Myval exactly (ie, the first integer file) 10

Now in the next line of code:

	++input;
  
  

VS2008 and then look at the input members:

After ++ input, it becomes 0x00000000 a private members _Myistr! And eoff defined as a variable before!

And then the next line and see what output:

	cout<<(in == eoff ? "EOF" : "others")<<endl;
  
  

Obviously at this time in == eoff set up, the resulting output is "EOF"  

Now that we know (input, eoff, back_inserter (ivec) such usage reasons copy of it. Because the copy function is more equality through the first input and eoff, such as if it will dereference (* input) is inserted into the ivec At last

Since then plus 1, and then compared with eoff. Until the end of relatively equal eoff! Therefore, the use of unused istream_iterator stream initialized as sentinels.

copy (istream_iterator <int> (cin), istream_iterator <int> (), back_inserter (ivec) is the same case. At the end of pressing need to generate the EOF flag ctrl + z ^ z

Complete procedure is as follows:

  
  
#include <iostream>
#include <vector>
#include <fstream>
#include <iterator> //istream_iterator,ostream_iterator,back_inserter
#include <algorithm> //copy
#include <Windows.h> //system
using namespace std;
int main()
{
istream_iterator< int> eoff;
ifstream infile ( "f: \\ test.txt" ) ; // Before running, please let f: \\ test.txt there is only one integer
istream_iterator< int> input(infile);
cout<< "the first element:"<<*input<< endl;
++input;
cout<<(input == eoff ? "EOF" : "others")<< endl;

cout<< "*******************"<< endl;
COUT << "Please enter an integer, press ctrl + z End Input:" << endl ;
vector< int> ivec;
copy(istream_iterator< int>( cin),istream_iterator< int>(),back_inserter(ivec));
// next sentence is the content output screen ivec
copy(ivec.begin(),ivec.end(),ostream_iterator< int>( cout, "\t"));
system( "pause");
}
  
  

ps: istream_iterator ostream_iterator are not defined and decrement, i.e. --input; is wrong!

2. Note that if for istream_iterator <int> type, if there is a file for the letter, then, input will happen then? 

Prior to this, please f: \ test.txt plus a letter and see what that is, content: 10 sfd (EOF)

  
  
istream_iterator< int> eoff;
ifstream infile ( "f: \\ test.txt" ) ; // Before running, please let f: \\ test.txt there is only one integer
istream_iterator< int> input(infile);
cout<< "the first element:"<<*input<< endl;
++input;
  
  

After a few runs this, istream_iterator <int> input (infile) should only point to integer, but now for the letter, and how will it?

We look at the input of the members present:

input the face of the letter, _Myistr also become a 0x00000000. So do not say

	cout<<(input == eoff ? "EOF" : "others")<<endl;
  
  

Will enter "EOF", that is, input == eoff it? The answer is yes indeed!

In fact, at this time cin.good () also is false, we can add a line of code to try: cout << cin.good () << endl;

Now we know that when only integer, use istream_iterator <int> (cin) input, you can enter a non-int type of letter to terminate input.

For ostream_iterator <T> ouput (strm, "xxx"); it is the same, but now the left output values:

E.g:

  
  
ostream_iterator< int> output( cout, " : ");
*output = 5;
*output = 6;
  
  

Or write

  
  
ostream_iterator< int> output( cout, " : ");
*output++ = 5;
*output++ = 6;
  
  

The results are: 5: 6

output dereference * After each assignment after output, will make their own self plus one.

That is not their own use of the method * output ++.

In short:

These two are the best to use:

  
  
copy(istream_iterator< int>( cin),istream_iterator< int>(),back_inserter(ivec));
// next sentence is the content output screen ivec
copy(ivec.begin(),ivec.end(),ostream_iterator< int>( cout, "\t"));
  
  

Enter the phrase is better

vector<int> ivec(istream_iterator<int>(cin),istream_iterator<int>());

Sentence more concise.

If the write-in question, please enlighten you heroes.

Please indicate the source.