New submission from Andrew V. Jones <andrewvaugh...@gmail.com>:
With Python 3.9.4, and when compiling with Visual Studio 2019, we have noticed
that the variable `_Py_ctype_table` is *not* scoped with in an `extern "C"`
block, and where the Python library (`python39.lib`) *has* been compiled with a
C compiler.
This causes an issue when trying to refer to `_Py_ctype_table` from a C++ file,
as the compiler tries to name-mangle the _use_ of `_Py_ctype_table`, but the
linker cannot then tie the mangled name to non-mangled named from
`python39.lib`.
Example:
```
#include "Python.h"
int main() { return _Py_ctype_table[0]; }
```
Compilation:
```
cl.exe /Fe:test.exe /TP /I include test.cpp /link libs/python39.lib
Microsoft (R) C/C++ Optimizing Compiler Version 19.28.29336 for x64
Copyright (C) Microsoft Corporation. All rights reserved.
test.cpp
Microsoft (R) Incremental Linker Version 14.28.29336.0
Copyright (C) Microsoft Corporation. All rights reserved.
/out:test.exe
libs/python39.lib
test.obj
test.obj : error LNK2019: unresolved external symbol "__declspec(dllimport)
unsigned int const * const _Py_ctype_table" (__imp_?_Py_ctype_table@@3QBIB)
referenced in function main
test.exe : fatal error LNK1120: 1 unresolved externals
```
With `cl.exe`:
```
cl.exe /Bv
Microsoft (R) C/C++ Optimizing Compiler Version 19.28.29336 for x64
Copyright (C) Microsoft Corporation. All rights reserved.
Compiler Passes:
Z:\home\avj\visual_studio\MSVC\14.28.29333\bin\HostX64\x64\cl.exe:
Version 19.28.29336.0
Z:\home\avj\visual_studio\MSVC\14.28.29333\bin\HostX64\x64\c1.dll:
Version 19.28.29336.0
Z:\home\avj\visual_studio\MSVC\14.28.29333\bin\HostX64\x64\c1xx.dll:
Version 19.28.29336.0
Z:\home\avj\visual_studio\MSVC\14.28.29333\bin\HostX64\x64\c2.dll:
Version 19.28.29336.0
Z:\home\avj\visual_studio\MSVC\14.28.29333\bin\HostX64\x64\c1xx.dll:
Version 19.28.29336.0
Z:\home\avj\visual_studio\MSVC\14.28.29333\bin\HostX64\x64\link.exe:
Version 14.28.29336.0
Z:\home\avj\visual_studio\MSVC\14.28.29333\bin\HostX64\x64\mspdb140.dll:
Version 14.28.29336.0
Z:\home\avj\visual_studio\MSVC\14.28.29333\bin\HostX64\x64\1033\clui.dll:
Version 19.28.29336.0
```
A naïve check of Python.h (e126547c07) seems to suggest that:
* There are 82 includes
* 64 of these contain `extern "C"`
* 8 do not contain `extern "C"`
* The remaining 10 are either system includes or pyconfig.h
For the 8 that *do not* contain `extern "C"`, none of these use `PyAPI_DATA`.
This leads me to believe that it is an oversight that `pyctype.h` does not have
`extern "C"`
----------
messages: 390855
nosy: andrewvaughanj
priority: normal
severity: normal
status: open
title: Missing 'extern "C"' for _Py_ctype_table
versions: Python 3.9
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue43816>
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