27.basic.ios.tie.stdcxx-804.cpp

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#include <cassert>
#include <cstddef>
#include <cstdio>
#include <sstream>
 
// tie the first n streams together in a circular list
void tie (std::ostringstream *ps, std::size_t n)
{
    for (std::size_t i = 0; i + 1 < n; ++i)
        ps [i].tie (ps + i + 1);
 
    if (n) {
        std::ostream *plast = ps + (n - 1);
        plast->tie (ps);
    }
}
 
 
// detect a cycle in a list of tied streams
bool is_cycle (const std::ostream *ps)
{
    if (0 == ps)
        return false;
 
    const std::ostream *p0, *p1;
 
    for (p0 = ps, p1 = ps->tie (); p0 && p1;
         p0 = p0->tie (), p1 = p1->tie () ? p1->tie ()->tie () : 0)
        if (p0 == p1 || p0->rdbuf () == p1->rdbuf ())
            return true;
 
    return false;
}
 
int main ()
{
    std::ostringstream strm [32];
    const std::size_t N = sizeof strm / sizeof *strm;
 
    for (std::size_t i = 0; i != N; ++i) {
 
        // tie the first i streams together in a circular list
        tie (strm, i);
 
        assert (0 == i || is_cycle (strm));
 
        for (std::size_t j = 0; j != i; ++j) {
 
            // make sure formatted and unformatted output for
            // each of the tied streams works without getting
            // into a deadlock or into infinite recursion
            strm [j] << j;
            strm [j].flush ();
 
            assert (strm [j].good ());
        }
    }
 
    return 0;
}