C++ - хочу прочитать содержимое std::string не копируя его куда-либо через интерфейс operator>>.

#include <streambuf>
#include <istream>
#include <string>

class string_istream : public std::istream {

    struct string_buf : public std::streambuf {
        string_buf(std::string &s) { setg(&*s.begin(), &*s.begin(), &*s.end()); }
    };

    string_buf sb;

public:

    string_istream(std::string &s) : std::istream(&sb), sb(s) {}

};

#include <cstdio>
#include <sstream>

int main()
{
    std::string s = "12345";
#ifdef SS
    std::istringstream ss(s);
#else
    string_istream ss(s);
#endif
    while (ss.good()) {
        char c;
        ss >> c;
        printf("%c\n", c);
    }
}

/*
➜  ~  g++ str.cc
➜  ~  valgrind ./a.out
==2533== Memcheck, a memory error detector
==2533== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==2533== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==2533== Command: ./a.out
==2533== 
1
2
3
4
5
5
==2533== 
==2533== HEAP SUMMARY:
==2533==     in use at exit: 0 bytes in 0 blocks
==2533==   total heap usage: 1 allocs, 1 frees, 30 bytes allocated
==2533== 
==2533== All heap blocks were freed -- no leaks are possible
==2533== 
==2533== For counts of detected and suppressed errors, rerun with: -v
==2533== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)
➜  ~  g++ -DSS str.cc 
➜  ~  valgrind ./a.out
==2544== Memcheck, a memory error detector
==2544== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==2544== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==2544== Command: ./a.out
==2544== 
1
2
3
4
5
5
==2544== 
==2544== HEAP SUMMARY:
==2544==     in use at exit: 0 bytes in 0 blocks
==2544==   total heap usage: 2 allocs, 2 frees, 60 bytes allocated
==2544== 
==2544== All heap blocks were freed -- no leaks are possible
==2544== 
==2544== For counts of detected and suppressed errors, rerun with: -v
==2544== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)
*/

string_buf(std::string &s) { setg(&*s.begin(), &*s.begin(), &*s.begin() + s.size()); }

#include <streambuf>
#include <istream>
#include <string>

class string_istream : public std::istream {

    struct string_buf : public std::streambuf {

        string_buf(std::string &s) {
            char *cs = &s[0];
                    // &*s.begin();
                    // const_cast<char*>(s.data());
            setg(cs, cs, cs + s.size());
        }

    };

    string_buf sb;

public:

    string_istream(std::string &s) : std::istream(&sb), sb(s) {}

};

#include <cstdio>

int main()
{
    std::string s = "0";
    string_istream ss(s);

    for (int i = 0; i < 10; ++i) {
        printf("%p %c\n", &s[0], ss.peek());
        s.append("1");
    }

}

/*
==2376== Memcheck, a memory error detector
==2376== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==2376== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==2376== Command: ./a.out
==2376== 
0x59f9058 0
==2376== Invalid read of size 1
==2376==    at 0x4EB7352: std::istream::peek() (in /usr/lib64/gcc/x86_64-pc-linux-gnu/4.7.3/libstdc++.so.6.0.17)
==2376==    by 0x401782: main (in /ht/a.out)
==2376==  Address 0x59f9058 is 24 bytes inside a block of size 26 free'd
==2376==    at 0x4C2AF3C: operator delete(void*) (vg_replace_malloc.c:480)
==2376==    by 0x4EF4607: std::string::reserve(unsigned long) (in /usr/lib64/gcc/x86_64-pc-linux-gnu/4.7.3/libstdc++.so.6.0.17)
==2376==    by 0x4EF4894: std::string::append(char const*, unsigned long) (in /usr/lib64/gcc/x86_64-pc-linux-gnu/4.7.3/libstdc++.so.6.0.17)
==2376==    by 0x4017BA: main (in /ht/a.out)
==2376== 
0x59f90b8 0
0x59f9118 0
0x59f9118 0
0x59f9178 0
0x59f9178 0
0x59f9178 0
0x59f9178 0
0x59f91e8 0
0x59f91e8 0
==2376== 
==2376== HEAP SUMMARY:
==2376==     in use at exit: 0 bytes in 0 blocks
==2376==   total heap usage: 5 allocs, 5 frees, 156 bytes allocated
==2376== 
==2376== All heap blocks were freed -- no leaks are possible
==2376== 
==2376== For counts of detected and suppressed errors, rerun with: -v
==2376== ERROR SUMMARY: 9 errors from 1 contexts (suppressed: 2 from 2)
*/

std::string s(...);
istringstream ss(s);