Accessing std::cout and std::cin from within gdb.

[Delcypher <delcypher@gmail.com>]

Hi I'm having problems accessing the cout and cin objects from within
gdb. If I take a simple example program:

#include <iostream>

using namespace std;
int main()
{
        ostream& mockCout = cout;
        istream& mockCin = cin;

        cout << "&std::cout is " << &cout << endl;
        cout << "&std::cin  is " << &cin << endl;

        cout << "&mockCin is " << &mockCin << endl;
        cout << "&mockCout  is " << &mockCout << endl;
        return 0;
}

And build with `g++ -Wall -g test.cpp' and then run `gdb a.out'

(gdb) b main
Breakpoint 1 at 0x40087c: file test.cpp, line 6.
(gdb) run
Starting program: /home/dan/src/a.out

Breakpoint 1, main () at test.cpp:6
6               ostream& mockCout = cout;
(gdb) n
7               istream& mockCin = cin;
(gdb) n
9               cout << "&std::cout is " << &cout << endl;
(gdb) n
&std::cout is 0x6013a0
10              cout << "&std::cin  is " << &cin << endl;
(gdb) n
&std::cin  is 0x601280
12              cout << "&mockCin is " << &mockCin << endl;
(gdb) n
&mockCin is 0x601280
13              cout << "&mockCout  is " << &mockCout << endl;
(gdb) n
&mockCout  is 0x6013a0
14              return 0;
(gdb) p &cout
$1 = (std::ostream *) 0x7ffff7dc9d60
(gdb) p &cin
$2 = (std::istream *) 0x7ffff7dc9e80
(gdb) p &mockCout
$3 = (std::ostream *) 0x6013a0
(gdb) p &mockCin
$4 = (std::istream *) 0x601280
(gdb)

What I see is that gdb has the completely wrong address for the cin
and cout objects. My references have the right address though.
Consequently calling any of cin's or cout's methods fails but using my
references works fine (except for the error messages I see).

(gdb) call cout.good()
Cannot access memory at address 0xffffffffffffffe8
(gdb) call mockCout.good()
warning: RTTI symbol not found for class 'std::ostream'
warning: RTTI symbol not found for class 'std::ostream'
warning: RTTI symbol not found for class 'std::ostream'
warning: RTTI symbol not found for class 'std::ostream'
warning: RTTI symbol not found for class 'std::ostream'
$6 = true
(gdb)

I found an old post
(http://sourceware.org/ml/gdb/2006-08/msg00244.html ) from over 5
years ago that demonstrates this behaviour and shows another way to
access cout or cin. In my case I could run

(gdb) call ( (std::ostream) *(0x6013a0)).good()



Is this behaviour of not being able to access cout and cin a bug or
have I done something wrong?

If needed here is some version information.
OS: Arch Linux x86_64
g++ version:  g++ (GCC) 4.6.1 20110819 (prerelease)
gdb version:  GNU gdb (GDB) 7.3.1

Thanks,
Dan.