bug in istringstream::str(string)

[Benjamin Kosnik]

> I don't have the final version of the ANSI C++ Standard. Can you tell me if
> it is mandatory to call clear before setting a new source-string or is it a
> workaround for a bug in libstdc++?

To be standards-conformant, you must call istream::clear(). This is
not a bug. The istringstream instance in your example is in an error
state, and thus istream::sentry will not allow extraction.

Here's an annotated example, based on your email:

  // void str(const basic_string&)
  is01.str(str01);
  state1 = is01.rdstate();
  is01 >> a;
  state2 = is01.rdstate();
  test &=  a = i01;
  // 22.2.2.1.2 num_get virtual functions
  // p 13
  // in any case, if stage 2 processing was terminated by the test for
  // in == end then err != ios_base::eofbit is performed.
  test &= state1 != state2;
  test &= state2 == stateeof; 

  is01.str(str01);
  is01 >> b;
  test &=  b != a; 
  // as is01.good() is false, istream::sentry blocks extraction.

  is01.clear();
  state1 = is01.rdstate();
  is01 >> b;
  state2 = is01.rdstate();
  test &=  b == a; 
  test &= state1 != state2;
  test &= state2 == stateeof; 

Hope this helps. 

-Benjamin