Fix compilation issues on macOS by conditionally undefining ctype macros #296
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…to avoid libstdc++ <locale> clashes
On older Apple toolchains (e.g., macOS 10.7.4/Xcode 4.3.3 with libstdc++ 4.2.1),
including <Python.h> pulls in <ctype.h>, which defines macros like isspace/isalnum.
When C++ headers such as <locale> (transitively included by moc-generated code)
declare the templated overloads (e.g., `bool std::isspace(_CharT, const std::locale&)`),
those C macros expand and break compilation with errors.
In `PythonQtPythonInclude.h`, explicitly `#undef` the problematic <ctype.h> macros
(isalnum, isalpha, islower, isspace, isupper, tolower, toupper) after including Python
headers. This keeps macro pollution out of downstream C++ includes and lets the std:: functions/
overloads compile cleanly.
It fixes error like the following:
```
/usr/include/c++/4.2.1/bits/localefwd.h:57:21: error:
too many arguments provided to function-like macro invocation
isspace(_CharT, const locale&);
```
```
moc_PythonQtStdDecorators.cxx:152:25:
error: expected unqualified-id
case 4: _t->emit((*reinterpret_cast<
QObject*(*)>(_a[1])),(*reinterpret_cast< const
`
```
(cherry picked from commit commontk/PythonQt@4ce028d)
… macOS C++ builds CPython’s `pyport.h` defines `_PY_PORT_CTYPE_UTF8_ISSUE` on macOS to work around BSD libc ctype behavior in UTF-8 locales. Those ctype names can surface as macros and collide with libstdc++’s `<locale>` templated overloads (e.g., `std::isspace`), leading to compilation errors. Previously we unconditionally `#undef`’d several ctype macros. Restrict this to the affected environment by guarding with `_PY_PORT_CTYPE_UTF8_ISSUE` and `__cplusplus`. This keeps macOS C++ builds healthy while avoiding unnecessary macro tampering elsewhere. Adapted from Kitware/VTK@a4fa448099 ("Remove the toupper macro defined by Python.h.", 2015-11-12).
| // Avoid clashes with libstdc++ <locale> by undefining ctype macros | ||
| // that CPython may introduce on macOS when the UTF-8 ctype quirk is enabled. | ||
| // (_PY_PORT_CTYPE_UTF8_ISSUE is defined by CPython’s pyport.h; we apply these | ||
| // undefs only in C++ builds.) |
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Interesting. Searching for this reveals a number of similar issues in CPython itself, which they seem to have resolved by using the macros from pyctype.h like Py_ISALPHA etc.
mrbean-bremen
approved these changes
Sep 4, 2025
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This pull request addresses compilation issues on older macOS toolchains caused by ctype macros defined by
<Python.h>. The changes include:isalnum,isalpha,islower,isspace,isupper,tolower,toupper) after including Python headers, to avoid clashes with C++ standard library headers like<locale>._PY_PORT_CTYPE_UTF8_ISSUEand__cplusplusmacros.Note
For reference, those patches were developed in the context of the
commontk/PythonQtfork.Cherry picked from commits commontk/PythonQt@4ce028d