[STDCXX-576] std::basic_streambuf<>::xsputn() incorrectly inserts the data, that is the part of the internal buffer - ASF JIRA

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The test below aborts on assert.

test.cpp:
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#include <sstream> // for stringbuf
#include <string> // for string
#include <cassert> // for assert()

struct PubBuf: std::stringbuf
{
char* Pbase () const

{ return this->pbase (); }

};

int main ()
{
// 512 is the default buffer size of the basic_stringbuf
std::string s (512, 'a');

std::stringbuf sbuf (s);
PubBuf& buf = (PubBuf&)sbuf;

std::streamsize res = buf.sputn (buf.Pbase (), 128);
s.append (s.begin (), s.begin () + 128);

const std::string& str = buf.str ();

assert (res == 128);
assert (str.size () == s.size ());
assert (str == s);

return 0;
}
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The test output:
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test: test.cpp:25: int main (): Assertion `str == s' failed.
Aborted
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