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fix string corruption in string_impl::shrink_to_fit #1176

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fix string corruption in string_impl::shrink_to_fit #1176

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5 changes: 3 additions & 2 deletions include/boost/json/detail/impl/string_impl.ipp
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Original file line number Diff line number Diff line change
Expand Up @@ -435,9 +435,10 @@ shrink_to_fit(
auto const t = p_.t;
if(t->size <= sbo_chars_)
{
char const* const p = data();
s_.k = short_string_;
std::memcpy(
s_.buf, data(), t->size);
s_.buf, p, t->size);
s_.buf[sbo_chars_] =
static_cast<char>(
sbo_chars_ - t->size);
Expand All @@ -458,7 +459,7 @@ shrink_to_fit(
std::memcpy(
tmp.data(),
data(),
size());
size() + 1);
destroy(sp);
*this = tmp;
#ifndef BOOST_NO_EXCEPTIONS
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32 changes: 32 additions & 0 deletions test/string.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1368,6 +1368,38 @@ class string_test
s.shrink_to_fit();
BOOST_TEST(s.capacity() < cap);
});

// shrink_to_fit() preserves the contents across reallocation
{
std::size_t const sbo = string{}.capacity();

// heap -> SBO: shrink a dynamic string down to fit in the SBO
{
std::string big(sbo * 3, '\0');
std::iota(big.begin(), big.end(), 'a');
string s(big.data(), big.size());
BOOST_TEST(s.capacity() > sbo);
std::size_t const n = sbo / 2;
s.resize(n);
s.shrink_to_fit();
BOOST_TEST(s.size() == n);
BOOST_TEST(s == string_view(big.data(), n));
BOOST_TEST(s.c_str()[s.size()] == '\0');
}

// heap -> smaller heap: still larger than the SBO after shrinking
{
std::string big(sbo * 4, '\0');
std::iota(big.begin(), big.end(), 'A');
string s(big.data(), big.size());
std::size_t const n = sbo * 2;
s.resize(n);
s.shrink_to_fit();
BOOST_TEST(s.size() == n);
BOOST_TEST(s == string_view(big.data(), n));
BOOST_TEST(s.c_str()[s.size()] == '\0');
}
}
}

void
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