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libstdc++: Disable std::string{,_view} construction from nullptr (P2166R1)

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Implement this C++23 feature. Because construction from a null pointer
is undefined, we can implement it for C++11 and up, turning undefined
behaviour into a compilation error.

libstdc++-v3/ChangeLog:

	* include/bits/basic_string.h (basic_string(nullptr_t)): Define
	as deleted.
	(operator=(nullptr_t)): Likewise.
	* include/bits/cow_string.h (basic_string(nullptr_t)): Likewise.
	(operator=(nullptr_t)): Likewise.
	* include/std/string_view (basic_string_view(nullptr_t)):
	Likewise.
	* testsuite/21_strings/basic_string/cons/char/nullptr.cc: New test.
	* testsuite/21_strings/basic_string_view/cons/char/nonnull.cc:
	Change dg-warning to dg-error.
	* testsuite/21_strings/basic_string_view/cons/wchar_t/nonnull.cc:
	Likewise.
This commit is contained in:
Jonathan Wakely 2021-10-01 21:27:24 +01:00
parent fa3ccf8bfe
commit cf876562c5
6 changed files with 13 additions and 2 deletions
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2
libstdc++-v3/include/bits/basic_string.h
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@ -623,6 +623,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
_M_construct(__str.begin(), __str.end());
}
basic_string(nullptr_t) = delete;
basic_string& operator=(nullptr_t) = delete;
#endif // C++11
/**

3
libstdc++-v3/include/bits/cow_string.h
View File

@ -667,6 +667,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
else
_M_dataplus._M_p = _S_construct(__str.begin(), __str.end(), __a);
}
basic_string(nullptr_t) = delete;
basic_string& operator=(nullptr_t) = delete;
#endif // C++11
/**

2
libstdc++-v3/include/std/string_view
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@ -168,6 +168,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#endif // C++23
#endif // C++20
basic_string_view(nullptr_t) = delete;
constexpr basic_string_view&
operator=(const basic_string_view&) noexcept = default;

4
libstdc++-v3/testsuite/21_strings/basic_string/cons/char/nullptr.cc Normal file
View File

@ -0,0 +1,4 @@
// { dg-do compile { target c++11 } }
#include <string>
std::string s = nullptr; // { dg-error "deleted" "P2166R1" }

2
libstdc++-v3/testsuite/21_strings/basic_string_view/cons/char/nonnull.cc
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@ -25,5 +25,5 @@ test01()
{
std::string_view s((const char*)nullptr); // { dg-warning "\\\[-Wnonnull" }
std::string_view t((char*)nullptr); // { dg-warning "\\\[-Wnonnull" }
std::string_view u(nullptr); // { dg-warning "\\\[-Wnonnull" }
std::string_view u(nullptr); // { dg-error "deleted" }
}

2
libstdc++-v3/testsuite/21_strings/basic_string_view/cons/wchar_t/nonnull.cc
View File

@ -25,5 +25,5 @@ test01()
{
std::wstring_view s((const wchar_t*)nullptr); // { dg-warning "\\\[-Wnonnull" }
std::wstring_view t((wchar_t*)nullptr); // { dg-warning "\\\[-Wnonnull" }
std::wstring_view u(nullptr); // { dg-warning "\\\[-Wnonnull" }
std::wstring_view u(nullptr); // { dg-error "deleted" }
}