[RFC] libstdc++/7220

[Paolo Carlini]

Hi,

the following testcase, distilled from the PR, passes with 3.0.4 (and 
Dinkum), doesn't with 3.1 and current v3:

#include <sstream>
#include <cassert>

#define Is std::basic_istream<char,std::char_traits<char> >
#define It std::char_traits<char>
#define Al std::allocator<char>

int main(int, char *[])
{
  int res = 0;
  std::streamsize n;
  std::basic_string<char,It,Al > input((const char *)"abcdefg\n");
  std::basic_stringbuf<char,It,Al > sbuf(input);
  std::basic_istream<char,It > istr(&sbuf);

  istr.ignore(0, (Is::int_type)'a');
  assert( istr.gcount() == 0 );

  return 0;
}

In your reading of the standard (27.6.1.3, 24), how ignore is supposed 
to behave in this case? When count == 0, and the next char is the 
delimiter ('a'), must it be eaten anyway or not?

Ciao, Paolo.