I cannot understand why the following code does not work. The compiler
displays the error
'x' undeclared (first use this function) in the sentance after the usung
namespace second; statement.
any will be appreciated .

#include <iostream>
using namespace std;

namespace first
{
int x = 5;
int y = 10;
}

namespace second
{
double x = 3.1416;
double y = 2.7183;
}

int main ()
{
using namespace first;
cout << x << endl;
cout << y << endl;
using namespace second;
cout << x << endl;
cout << y << endl;
system("pause");
}

On Dec 26, 9:42 pm, "Nikos Hatzigiannakis" <y...@aegean.gr> wrote:
> I cannot understand why the following code does not work. The compiler
> displays the error
> 'x' undeclared (first use this function) in the sentance after the usung
> namespace second; statement.
> any will be appreciated .
>
> #include <iostream>
> using namespace std;
>
> namespace first
> {
> int x = 5;
> int y = 10;
>
> }
>
> namespace second
> {
> double x = 3.1416;
> double y = 2.7183;
>
> }
>
> int main ()
> {
> using namespace first;
> cout << x << endl;
> cout << y << endl;
> using namespace second;
> cout << x << endl;
> cout << y << endl;
> system("pause");
>
> }

well i just get ambiguous symbol after using the second namespace...
but cout<<second::x<<endl; works...

On Wed, 26 Dec 2007 17:42:41 +0100, Nikos Hatzigiannakis <ypai@aegean.gr>
wrote:

> I cannot understand why the following code does not work. The compiler
> displays the error
> 'x' undeclared (first use this function) in the sentance after the usung
> namespace second; statement.
> any will be appreciated .
>
> #include <iostream>
> using namespace std;
>
> namespace first
> {
> int x = 5;
> int y = 10;
> }
>
> namespace second
> {
> double x = 3.1416;
> double y = 2.7183;
> }
>
> int main ()
> {
> using namespace first;
> cout << x << endl;
> cout << y << endl;
> using namespace second;
> cout << x << endl;
> cout << y << endl;
> system("pause");
> }
>
>
On Wed, 26 Dec 2007 17:42:41 +0100, Nikos Hatzigiannakis <ypai@aegean.gr>
wrote:

> I cannot understand why the following code does not work. The compiler
> displays the error
> 'x' undeclared (first use this function) in the sentance after the usung
> namespace second; statement.
> any will be appreciated .
>
> #include <iostream>
> using namespace std;
>
> namespace first
> {
> int x = 5;
> int y = 10;
> }
>
> namespace second
> {
> double x = 3.1416;
> double y = 2.7183;
> }
>
> int main ()
> {
> using namespace first;
> cout << x << endl;
> cout << y << endl;
> using namespace second;
> cout << x << endl;
> cout << y << endl;
> system("pause");
> }
>
>
When you use the second namepsace by the instruction "using namespace
second;" , the compiler don't know which x and y he should use.
Use first::x and second::y ? Use second::x and fisrt::y ? ....
It's Ambiguous. You must leave the ambiguity by first:: or second:: before
x and y after tou have written "using namespace second;"

So it become :

int main ()
{
using namespace first;
cout << x << endl;
cout << y << endl;
using namespace second;
cout << second::x << endl;
cout << second::y << endl;
system("pause");
}
However if the the second namespace have a member named z, you could do
cout << z << endl without ambiguity

(When i compile your code,i've ot the same error as you.)

On Dec 26, 10:07 pm, David Côme <davidc...@wanadoo.fr> wrote:
> On Wed, 26 Dec 2007 17:42:41 +0100, Nikos Hatzigiannakis <y...@aegean.gr>
> wrote:
>
>
>
> > I cannot understand why the following code does not work. The compiler
> > displays the error
> > 'x' undeclared (first use this function) in the sentance after the usung
> > namespace second; statement.
> > any will be appreciated .
>
> > #include <iostream>
> > using namespace std;
>
> > namespace first
> > {
> > int x = 5;
> > int y = 10;
> > }
>
> > namespace second
> > {
> > double x = 3.1416;
> > double y = 2.7183;
> > }
>
> > int main ()
> > {
> > using namespace first;
> > cout << x << endl;
> > cout << y << endl;
> > using namespace second;
> > cout << x << endl;
> > cout << y << endl;
> > system("pause");
> > }
>
> On Wed, 26 Dec 2007 17:42:41 +0100, Nikos Hatzigiannakis <y...@aegean.gr>
> wrote:
>
>
>
> > I cannot understand why the following code does not work. The compiler
> > displays the error
> > 'x' undeclared (first use this function) in the sentance after the usung
> > namespace second; statement.
> > any will be appreciated .
>
> > #include <iostream>
> > using namespace std;
>
> > namespace first
> > {
> > int x = 5;
> > int y = 10;
> > }
>
> > namespace second
> > {
> > double x = 3.1416;
> > double y = 2.7183;
> > }
>
> > int main ()
> > {
> > using namespace first;
> > cout << x << endl;
> > cout << y << endl;
> > using namespace second;
> > cout << x << endl;
> > cout << y << endl;
> > system("pause");
> > }
>
> When you use the second namepsace by the instruction "using namespace
> second;" , the compiler don't know which x and y he should use.
> Use first::x and second::y ? Use second::x and fisrt::y ? ....
> It's Ambiguous. You must leave the ambiguity by first:: or second:: before
> x and y after tou have written "using namespace second;"
>
> So it become :
>
> int main ()
> {
> using namespace first;
> cout << x << endl;
> cout << y << endl;
> using namespace second;
> cout << second::x << endl;
> cout << second::y << endl;
> system("pause");
> }
> However if the the second namespace have a member named z, you could do
> cout << z << endl without ambiguity
>
> (When i compile your code,i've ot the same error as you.)

And is there anyway to turn off a visible namespace?

On Dec 26, 12:09 pm, Rahul <sam_...@yahoo.co.in> wrote:
> On Dec 26, 10:07 pm, David Côme <davidc...@wanadoo.fr> wrote:
>
>
>
> > On Wed, 26 Dec 2007 17:42:41 +0100, Nikos Hatzigiannakis <y...@aegean.gr>
> > wrote:
>
> > > I cannot understand why the following code does not work. The compiler
> > > displays the error
> > > 'x' undeclared (first use this function) in the sentance after the usung
> > > namespace second; statement.
> > > any will be appreciated .
>
> > > #include <iostream>
> > > using namespace std;
>
> > > namespace first
> > > {
> > > int x = 5;
> > > int y = 10;
> > > }
>
> > > namespace second
> > > {
> > > double x = 3.1416;
> > > double y = 2.7183;
> > > }
>
> > > int main ()
> > > {
> > > using namespace first;
> > > cout << x << endl;
> > > cout << y << endl;
> > > using namespace second;
> > > cout << x << endl;
> > > cout << y << endl;
> > > system("pause");
> > > }
>
> > On Wed, 26 Dec 2007 17:42:41 +0100, Nikos Hatzigiannakis <y...@aegean.gr>
> > wrote:
>
> > > I cannot understand why the following code does not work. The compiler
> > > displays the error
> > > 'x' undeclared (first use this function) in the sentance after the usung
> > > namespace second; statement.
> > > any will be appreciated .
>
> > > #include <iostream>
> > > using namespace std;
>
> > > namespace first
> > > {
> > > int x = 5;
> > > int y = 10;
> > > }
>
> > > namespace second
> > > {
> > > double x = 3.1416;
> > > double y = 2.7183;
> > > }
>
> > > int main ()
> > > {
> > > using namespace first;
> > > cout << x << endl;
> > > cout << y << endl;
> > > using namespace second;
> > > cout << x << endl;
> > > cout << y << endl;
> > > system("pause");
> > > }
>
> > When you use the second namepsace by the instruction "using namespace
> > second;" , the compiler don't know which x and y he should use.
> > Use first::x and second::y ? Use second::x and fisrt::y ? ....
> > It's Ambiguous. You must leave the ambiguity by first:: or second:: before
> > x and y after tou have written "using namespace second;"
>
> > So it become :
>
> > int main ()
> > {
> > using namespace first;
> > cout << x << endl;
> > cout << y << endl;
> > using namespace second;
> > cout << second::x << endl;
> > cout << second::y << endl;
> > system("pause");
> > }
> > However if the the second namespace have a member named z, you could do
> > cout << z << endl without ambiguity
>
> > (When i compile your code,i've ot the same error as you.)
>
> And is there anyway to turn off a visible namespace?

namepaces aren't turned on or off.
You either provide access or you don't.
A far better system than an on/off toggle is scopes:

#include <iostream>

namespace test
{
int n;
}

void foo()
{
using namespace test;
std:: cout << "n = " << n << std::endl;
}

int main()
{
test::n = 0; // ok
// n = 99; // error
{ // anonymous scope
using namespace test;
n = 99;
}
// std:: cout << "n = " << n << std::endl; // error
foo();
}

On Dec 26, 11:42 am, "Nikos Hatzigiannakis" <y...@aegean.gr> wrote:
> I cannot understand why the following code does not work. The compiler
> displays the error
> 'x' undeclared (first use this function) in the sentance after the usung
> namespace second; statement.
> any will be appreciated .
>
> #include <iostream>
> using namespace std;
>
> namespace first
> {
> int x = 5;
> int y = 10;
>
> }
>
> namespace second
> {
> double x = 3.1416;
> double y = 2.7183;
>
> }
>
> int main ()
> {
> using namespace first;
> cout << x << endl;
> cout << y << endl;
> using namespace second;
> cout << x << endl;
> cout << y << endl;
> system("pause");
>
> }

Do not use using clause. it increases the chances of name conflicts.
Use fully qualified names.
e.g.
first::x;
second::x;

On 26 ÄÅË 2007, 22:09, Rahul <sam_...@yahoo.co.in> wrote:

> And is there anyway to turn off a visible namespace?

Just enclose using clause to a `compound operator':

{
using namespace first;
cout << x << endl;
cout << y << endl;
}
{
using namespace second;
cout << x << endl;
cout << y << endl;
}

On 3 Jan, 21:08, Pavel Shved <Pavel.Sh...@gmail.com> wrote:
> [stuff]

Sorry. :-( I wish this place had a delete button :-(