@@ -566,13 +566,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _Operation>
constexpr void
basic_string<_CharT, _Traits, _Alloc>::
- resize_and_overwrite(size_type __n, _Operation __op)
+ resize_and_overwrite(const size_type __n, _Operation __op)
{
const size_type __capacity = capacity();
_CharT* __p;
if (__n > __capacity)
{
- __p = _M_create(__n, __capacity);
+ auto __new_capacity = __n; // Must not allow _M_create to modify __n.
+ __p = _M_create(__new_capacity, __capacity);
this->_S_copy(__p, _M_data(), length()); // exclude trailing null
#if __cpp_lib_is_constant_evaluated
if (std::is_constant_evaluated())
@@ -580,7 +581,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#endif
_M_dispose();
_M_data(__p);
- _M_capacity(__n);
+ _M_capacity(__new_capacity);
}
else
__p = _M_data();
@@ -120,6 +120,26 @@ test05()
return true;
}
+void
+test06()
+{
+ std::string s = "0123456789";
+ s.resize_and_overwrite(16, [](char* p, int n) {
+ VERIFY( n == 16 );
+ std::char_traits<char>::copy(p + 10, "0123456798", 6);
+ return n;
+ });
+ VERIFY( s.size() == 16 );
+ VERIFY( s == "0123456789012345" );
+
+ s.resize_and_overwrite(4, [](char* p, int n) {
+ VERIFY( n == 4 );
+ std::char_traits<char>::copy(p, "abcd", 4);
+ return n;
+ });
+ VERIFY( s.size() == 4 );
+}
+
int main()
{
test01();
@@ -127,4 +147,5 @@ int main()
test03();
test04();
static_assert( test05() );
+ test06();
}
@@ -256,6 +256,11 @@ test_wchar()
std::locale loc;
s = std::format(loc, L"{:L} {:.3s}{:Lc}", true, L"data"sv, '.');
VERIFY( s == L"true dat." );
+
+ s = std::format(L"{}", 0.0625);
+ VERIFY( s == L"0.0625" );
+ s = std::format(L"{}", 0.25);
+ VERIFY( s == L"0.25" );
}
void
new file mode 100644
@@ -0,0 +1,4 @@
+// { dg-do run { target c++23 } }
+// This test does not have -std=gnu++20 in dg-options so that format.cc
+// can be tested for e.g. -std=c++26
+#include "format.cc"
Tested x86_64-linux, pushed to trunk. This should be backported to gcc-12 and gcc-13 too (without the std::format test changes). -- >8 -- The callable used for resize_and_overwrite was being passed the string's expanded capacity, which might be greater than the new size being requested. This is not conforming, as the standard requires the same n to be passed to the callable that the user passed to resize_and_overwrite. The existing tests didn't catch this because they all used a value which was more than twice the existing capacity, so the _M_create call allocated exactly what was requested, and the value passed to the callable was correct. But when the requested size is greater than the current capacity but smaller than twice the current capacity, _M_create will allocate twice the current capacity and then that value was being passed to the callable. I noticed this because std::format(L"{}", 0.25) was producing L"0.25XX" where the XX characters were whatever happened to be on the stack before the call. When std::format used resize_and_overwrite to widen a string it was copying too many characters into the destination and setting the result's length too long. I've added a test for this case, and a new test that doesn't hardcode -std=gnu++20 so can be used to test std::format in C++23 and C++26 modes. libstdc++-v3/ChangeLog: * include/bits/basic_string.tcc (resize_and_overwrite): Invoke the callable with the same size as resize_and_overwrite was called with. * testsuite/21_strings/basic_string/capacity/char/resize_and_overwrite.cc: Check with small values for the new size. * testsuite/std/format/functions/format.cc: Check wide formatting of double values that produce small strings. * testsuite/std/format/functions/format_c++23.cc: New test. --- libstdc++-v3/include/bits/basic_string.tcc | 7 ++++--- .../capacity/char/resize_and_overwrite.cc | 21 +++++++++++++++++++ .../testsuite/std/format/functions/format.cc | 5 +++++ .../std/format/functions/format_c++23.cc | 4 ++++ 4 files changed, 34 insertions(+), 3 deletions(-) create mode 100644 libstdc++-v3/testsuite/std/format/functions/format_c++23.cc