vector<string> gives error

[arnuld]

in C++ Primer 4/3 Lippman says in chapter 3, section 3.3.1:

vector<stringsv ec(10);
// 10 elements, each an empty string

here is the the code output & output from my Debian box running "gcc
3.3.5":

#include <iostream>
#include <vector>
#include <string>

int main() {
std::vector<str ingsvec(10);

// std::cout << v_str << std::endl;

return 0;
}
/* OUTPUT

unix@debian:~/programming/cpp$ g++ -ansi test-programme.cpp

test-programme.cpp: In function `int main()':
test-programme.cpp:6 : error: `string' undeclared (first use this
function)
test-programme.cpp:6 : error: (Each undeclared identifier is reported
only once
for each function it appears in.)
test-programme.cpp:6 : error: template argument 1 is invalid
test-programme.cpp:6 : error: template argument 2 is invalid
test-programme.cpp:6 : error: ISO C++ forbids declaration of `svec' with
no type

unix@debian:~/programming/cpp$

*/
where is the trouble?

"arnuld"

[Sumit Rajan]

arnuld wrote:

in C++ Primer 4/3 Lippman says in chapter 3, section 3.3.1:

vector<stringsv ec(10);
// 10 elements, each an empty string

here is the the code output & output from my Debian box running "gcc
3.3.5":

#include <iostream>
#include <vector>
#include <string>

int main() {
std::vector<str ingsvec(10);

std::vector<std ::stringsvec(10 );

>
// std::cout << v_str << std::endl;

return 0;
}
/* OUTPUT

unix@debian:~/programming/cpp$ g++ -ansi test-programme.cpp

test-programme.cpp: In function `int main()':
test-programme.cpp:6 : error: `string' undeclared (first use this
function)
test-programme.cpp:6 : error: (Each undeclared identifier is reported
only once
for each function it appears in.)
test-programme.cpp:6 : error: template argument 1 is invalid
test-programme.cpp:6 : error: template argument 2 is invalid
test-programme.cpp:6 : error: ISO C++ forbids declaration of `svec' with
no type

Regards,
Sumit.

[arnuld]

Sumit Rajan wrote:

std::vector<str ingsvec(10);

std::vector<std ::stringsvec(10 );

OK, i even tried "using std::vector" but still same error was reported.
it means, C++ Primer is wrong here.

anyway, what exactly "std::vector<st ringsvec;" &
"std::vector<st d::stringsvec;" say to the compiler?

[Ney André de Mello Zunino]

arnuld wrote:

OK, i even tried "using std::vector" but still same error was reported.
it means, C++ Primer is wrong here.

That would bring only the /vector/ symbol into scope.

anyway, what exactly "std::vector<st ringsvec;" &

The above is an attempt to instantiate the /std::vector/ template using
a type /string/ as its template parameter. If the compiler can see no
type named /string/ in scope at the point of instantiation, the
instantiation will fail.

"std::vector<st d::stringsvec;" say to the compiler?

This time you are using /std::string/ as the template parameter. The
difference is that you are letting the compiler know that the /string/
type actually lives inside the /std/ namespace and not in the global
namespace.

FWIW, your first attempt would have worked out if you had included a
/using std::string;/ statement before the instantiation.

Regards,

--
Ney André de Mello Zunino

[arnuld]

Ney André de Mello Zunino wrote:

OK, i even tried "using std::vector" but still same error was reported.
it means, C++ Primer is wrong here.

That would bring only the /vector/ symbol into scope.

ok, i got it.

This time you are using /std::string/ as the template parameter. The
difference is that you are letting the compiler know that the /string/
type actually lives inside the /std/ namespace and not in the global
namespace.

FWIW, your first attempt would have worked out if you had included a
/using std::string;/ statement before the instantiation.

Hmmm.. that is why /std::vector<int >/ works as /int/ is already in
global namespace

now i understood.
also why this works: /std::vector<int >::iterator/ & why using
/std::vector<int >::std::iterato r/ gives error?

please do not get angry, i am a newbie :-(

"arnuld"

[Howard]

"arnuld" <ar*****@gmail. comwrote in message
news:11******** *************@i 42g2000cwa.goog legroups.com...
Ney Andri de Mello Zunino wrote:

also why this works: /std::vector<int >::iterator/ & why using
/std::vector<int >::std::iterato r/ gives error?

Because :: indicates membership (either of a class or of a namespace), and
std is not a member of std::vector<>. So, using ::std::iterator is an
error. However, iterator is a member, so using ::iterator is correct.

-Howard

[LR]

arnuld wrote:

>

also why this works: /std::vector<int >::iterator/ & why using
/std::vector<int >::std::iterato r/ gives error?

Think of having a struct like:

namespace non_std {
struct S {
typedef int my_type;
};
}

and somewhere else in your code you have:
const non_std::S::my_ type i = 43;

where (informally)
non_std is a namespace
S is a struct in the namespace non_std
my_type is a typedef in the struct S

And how that might differ from:

const non_std::S::non _std::my_type i = -1;
^^^^^^^
What is this?

Same thing for std::vector<int >::iterator

(informally)
std is a namespace.
vector<intis the name of a class.
iterator is a type that is a member of the class vector<int>

OTOH, You could do something like this:

namespace non_std {
struct S {
struct non_std {
typedef int my_type;
};
};
}

and then
const non_std::S::non _std::my_type i = 99;

Confusing? Yes. Don't do that.

please do not get angry, i am a newbie :-(

Ok.

LR

[Martin Steen]

arnuld wrote:

#include <iostream>
#include <vector>
#include <string>

// insert this line here:
using namespace std;

>
int main() {
std::vector<str ingsvec(10);

// std::cout << v_str << std::endl;

return 0;
}

Best regards, Martin

[arnuld]

Martin Steen wrote:

#include <iostream>
#include <vector>
#include <string>

// insert this line here:
using namespace std;

it seems like you do not read C++ FAQs:

http://www.parashift.com/c++-faq-lit....html#faq-27.5

i did check them before i posted my problem.

thanks

"arnuld" -- www.arnuld.blogspot.com

[Noah Roberts]

arnuld wrote:

Martin Steen wrote:

#include <iostream>
#include <vector>
#include <string>

// insert this line here:
using namespace std;

it seems like you do not read C++ FAQs:

http://www.parashift.com/c++-faq-lit....html#faq-27.5

i did check them before i posted my problem.

Nice, someone answers your question and you respond flippantly.

Oh well. Don't qualify your namespaces then. See how far it gets yah.