[libcxx-bugs] Incoherent behaviour on integer overflow
phiippe dunski via libcxx-bugs
libcxx-bugs at lists.llvm.org
Sat Dec 14 06:35:48 PST 2019
Hello,
I'm not sure that this mail should really have to be sent on this list,
Maybe should I report this to specific clang mailing list. But, I hope you
put me on the right way...
Here is the overflow_error.cpp which contains what I expected to be 16
error case when using std::integral_constant.
The point was, for me, perfectly clear : for each integer type, if I try to
define some constant whose value is std::numeric_limits<the_type>::min()-1
or std::numeric_limits<the_type>::max() + 1, I should get the same
behaviour : at least some compile time warning, or mabe even some compile
time error.
Having two error cases for each data type, and eight data types, I was
expecting to get ... sixteen error when trying to compile this file.
But, as you can see it in the error_output.txt, they are only fourteen
errors:
using std::numeric_limits<uint32_t>::max() +1 and
std::numeric_limits<uint64_t>::max() + 1 do not produce the same behaviour
than usigne other data types or values.
IMHO, there is some incoherence behind that. Isn't it?
PS: Please forgive my poor English, but my mother tongue is French
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overflow_erro.cpp:4:57: error: non-type template argument evaluates to -129, which cannot be narrowed to type 'signed char' [-Wc++11-narrowing]
using Int8MinError = std::integral_constant<std::int8_t,std::numeric_limits<std::int8_t>::min()-1>;
^
overflow_erro.cpp:5:59: error: non-type template argument evaluates to -32769, which cannot be narrowed to type 'short' [-Wc++11-narrowing]
using Int16MinError = std::integral_constant<std::int16_t,std::numeric_limits<std::int16_t>::min()-1>;
^
overflow_erro.cpp:6:59: error: non-type template argument is not a constant expression
using Int16MinError = std::integral_constant<std::int32_t,std::numeric_limits<std::int32_t>::min()-1>;
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
overflow_erro.cpp:6:99: note: value -2147483649 is outside the range of representable values of type 'int'
using Int16MinError = std::integral_constant<std::int32_t,std::numeric_limits<std::int32_t>::min()-1>;
^
overflow_erro.cpp:7:59: error: non-type template argument is not a constant expression
using Int16MinError = std::integral_constant<std::int64_t,std::numeric_limits<std::int64_t>::min()-1>;
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
overflow_erro.cpp:7:99: note: value -9223372036854775809 is outside the range of representable values of type 'long'
using Int16MinError = std::integral_constant<std::int64_t,std::numeric_limits<std::int64_t>::min()-1>;
^
overflow_erro.cpp:10:57: error: non-type template argument evaluates to 128, which cannot be narrowed to type 'signed char' [-Wc++11-narrowing]
using Int8MaxError = std::integral_constant<std::int8_t,std::numeric_limits<std::int8_t>::max() + 1>;
^
overflow_erro.cpp:11:59: error: non-type template argument evaluates to 32768, which cannot be narrowed to type 'short' [-Wc++11-narrowing]
using Int16MaxError = std::integral_constant<std::int16_t,std::numeric_limits<std::int16_t>::max() + 1>;
^
overflow_erro.cpp:12:59: error: non-type template argument is not a constant expression
using Int32MaxError = std::integral_constant<std::int32_t,std::numeric_limits<std::int32_t>::max() + 1>;
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
overflow_erro.cpp:12:100: note: value 2147483648 is outside the range of representable values of type 'int'
using Int32MaxError = std::integral_constant<std::int32_t,std::numeric_limits<std::int32_t>::max() + 1>;
^
overflow_erro.cpp:13:59: error: non-type template argument is not a constant expression
using Int64MaxError = std::integral_constant<std::int64_t,std::numeric_limits<std::int64_t>::max() + 1>;
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
overflow_erro.cpp:13:100: note: value 9223372036854775808 is outside the range of representable values of type 'long'
using Int64MaxError = std::integral_constant<std::int64_t,std::numeric_limits<std::int64_t>::max() + 1>;
^
overflow_erro.cpp:16:59: error: non-type template argument evaluates to -1, which cannot be narrowed to type 'unsigned char' [-Wc++11-narrowing]
using UInt8MinError = std::integral_constant<std::uint8_t,-1>;
^
overflow_erro.cpp:17:61: error: non-type template argument evaluates to -1, which cannot be narrowed to type 'unsigned short' [-Wc++11-narrowing]
using UInt16MinError = std::integral_constant<std::uint16_t,-1>;
^
overflow_erro.cpp:18:61: error: non-type template argument evaluates to -1, which cannot be narrowed to type 'unsigned int' [-Wc++11-narrowing]
using UInt32MinError = std::integral_constant<std::uint32_t,-1>;
^
overflow_erro.cpp:19:61: error: non-type template argument evaluates to -1, which cannot be narrowed to type 'unsigned long' [-Wc++11-narrowing]
using UInt64MinError = std::integral_constant<std::uint64_t,-1>;
^
overflow_erro.cpp:22:59: error: non-type template argument evaluates to 256, which cannot be narrowed to type 'unsigned char' [-Wc++11-narrowing]
using UInt8MaxError = std::integral_constant<std::uint8_t,std::numeric_limits<std::uint8_t>::max() + 1>;
^
overflow_erro.cpp:23:61: error: non-type template argument evaluates to 65536, which cannot be narrowed to type 'unsigned short' [-Wc++11-narrowing]
using UInt16MaxError = std::integral_constant<std::uint16_t,std::numeric_limits<std::uint16_t>::max() + 1>;
^
14 errors generated.
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