seek from end of a istringstream fails

Question

Here is a minimalist code :

#include <string>
#include <sstream>
#include <iostream>

int main ()
    {
    std::string str = "spam" ;
    std::istringstream isz( str ) ;
    isz.seekg( 1,std::ios_base::beg ) ; std::cout << isz.fail() ;
    isz.seekg( 1,std::ios_base::cur ) ; std::cout << isz.fail() ;
    isz.seekg( 1,std::ios_base::end ) ; std::cout << isz.fail() ;
    return 0 ;
    }

I get 001 meaning the last seekg failed.
I the same with linux/g++ and win/MSVC.
I can't find such limitation in C++/stl documentation...
Any idea ?
Thx

Answer 1

Sorry, I missed a point :
When I call seekg( 1,std::ios_base::end ), I try go 1 char after the end (which fails as it should).
I have to call seekg( -1,std::ios_base::end ) to go 1 char before the end.