How to refer to iostate?

[akilguo]

Hi, folks:
i have written a program that uses an iostream member type iostate, i worte some code like those at the beginning of source file, but it seems wrong:

#include<istream>
using istream::iostate

how can i refer to it? Thanks!

[akilguo]

does anybody know that? The iostate is a Standard library member type defined in ios_base header, but i don't know how to include it in my program, i would appreciate it very much if you tell me... well , all i want is to output the size of the iostate, i wrote some thing like this:

#include<iostream>
#include<istream>
using std::cin;
using std::cout;
using std::endl;
int main()
{
int num;
cout << "Please enter a integer: " << endl;
cin >> num;
if(cin.good() )cout << "The integer is: " << num <<endl;
else {
istream::iostate state = cin.rdstate();
cout << state << endl;
}
return 0;
}

All i want is to output the state of cin! But when i compile, the compiler tells me " istream has not been declared! iostate was not declared in this scope! " What's wrong? anyone helps! Thanks!

[guestgulkan]

That's because it is such an easy fix, we were letting letting you find it for yourself.

Because as you said, it is in the std library.

[akilguo]

Do you mean i should write " using std::iostate " at the beginning of my source file? it didn't work, i tried...

[guestgulkan]

std::istream::iostate state = cin.rdstate();

or you can write this:

using std::istream;

//other code
istream::iostate state = cin.rdstate()

;

[akilguo]

Thanks, guestgulkan, it works!
but there still is one problem remains:
why do i have to prefix iostate by istream:: in the expression statement when i have already used using declaration at the beginning of my source file? That is, why doesn't the following code work?

using std::istream;
iostate state = cin.rdstate();

i doubt this because after i declaredusing std::cin, i can use cin in expression statement directly! Can you tell me how i can use iostate directly? Thanks!

[guestgulkan]

I'd have to check through the varios headers, but if I remember correctly - iostate is a enum defined in the ios_base class which is inherited by istream and ostream

So iostate is not directly defined in the std namespace - that is why it is:
std::istream::iostate or std::ostream::iostate or std::ios_base::iostate,

but NOT std::iostate

[blackcoder41]

why do i have to prefix iostate by istream:: in the expression statement when i have already used using declaration at the beginning of my source file? That is, why doesn't the following code work?

That is because istream is a class name and not a namespace. Actually iostate is a member of ios_base, but you can access it through istream since it inherits it from ios, and which ios inherits from ios_base.
http://cplusplus.com/reference/iostream/

Can you tell me how i can use iostate directly?

You can define a new type.

using namespace std;
typedef ios_base::iostate iostate;

iostate state = cin.rdstate();

[akilguo]

Yeah, i see ...
i still have many questions about namespace , i will work harder. Thanks , you guys!