21.string.io.stdcxx-250.cpp

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#include <cassert>
#include <istream>
#include <string>
 
int main ()
{
    struct MyBuf : std::streambuf {
        int_type underflow () {
            static int i = 0;
            // i == 0: sgect() invoked from sentry ctor
            // i == 1: sgetc() invoked from operator>>()
            // i == 2: sbumpc() invoked from operator>>()
            return 1 < i++ ? throw i : 'x';
        }
    } buf;
 
    std::istream is (&buf);
 
    std::string s;
    is >> s;
 
    assert ("x" == s);
    assert ((is.failbit | is.badbit) == is.rdstate ());
 
    return 0;
}