Cygwin 下的 gcc 9.3.0 预处理器：cmdline -Dname 但名称似乎未定义

Question

我正在尝试在 Cygwin 下构建 OCRmyPDF 并将运行变成一块砖墙。虽然我的整个职业生涯都是开发人员，但我一直在工作主要在 Java 并且对 Python 内部结构和 C++ 知之甚少。对于这些领域的专家来说，这个问题可能是显而易见的，但我难倒了。

OCRmyPDF on Linux 作为一组 "wheel" 软件包安装。我收集了一个 wheel 是一个预构建的依赖包。由于某种原因，在 pip 安装程序 Cygwin 认为它不能使用 wheel bundles 并且想要从源头重建。尝试重建时出现问题 pikepdf包。

这是错误：

  building 'pikepdf._qpdf' extension
  creating build/temp.cygwin-3.1.4-x86_64-3.7
  creating build/temp.cygwin-3.1.4-x86_64-3.7/src
  creating build/temp.cygwin-3.1.4-x86_64-3.7/src/qpdf
  gcc -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -ggdb -O2 -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector-strong --param=ssp-buffer-size=4 -fdebug-prefix-map=/cygdrive/d/cyg_pub/devel/python/python37/python37-3.7.7-1.x86_64/build=/usr/src/debug/python37-3.7.7-1 -fdebug-prefix-map=/cygdrive/d/cyg_pub/devel/python/python37/python37-3.7.7-1.x86_64/src/Python-3.7.7=/usr/src/debug/python37-3.7.7-1 -ggdb -O2 -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector-strong --param=ssp-buffer-size=4 -fdebug-prefix-map=/cygdrive/d/cyg_pub/devel/python/python37/python37-3.7.7-1.x86_64/build=/usr/src/debug/python37-3.7.7-1 -fdebug-prefix-map=/cygdrive/d/cyg_pub/devel/python/python37/python37-3.7.7-1.x86_64/src/Python-3.7.7=/usr/src/debug/python37-3.7.7-1 -D__MISC_VISIBLE=1 -I/tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include -I/tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include -I/usr/include/python3.7m -c src/qpdf/annotation.cpp -o build/temp.cygwin-3.1.4-x86_64-3.7/src/qpdf/annotation.o -DVERSION_INFO="1.11.2" -std=c++14 -fvisibility=hidden
  In file included from src/qpdf/annotation.cpp:18:
  /tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include/pybind11/pybind11.h: In member function ‘void pybind11::cpp_function::initialize_generic(pybind11::detail::function_record*, const char*, const std::type_info* const*, pybind11::size_t)’:
  /tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include/pybind11/pybind11.h:197:21: error: ‘strdup’ was not declared in this scope; did you mean ‘strcmp’?
    197 |         rec->name = strdup(rec->name ? rec->name : "");
        |                     ^~~~~~
        |                     strcmp
  In file included from src/qpdf/annotation.cpp:18:
  /tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include/pybind11/pybind11.h: In member function ‘pybind11::class_<type_, options>& pybind11::class_<type_, options>::def_property_static(const char*, const pybind11::cpp_function&, const pybind11::cpp_function&, const Extra& ...)’:
  /tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include/pybind11/pybind11.h:1284:31: error: there are no arguments to ‘strdup’ that depend on a template parameter, so a declaration of ‘strdup’ must be available [-fpermissive]
   1284 |               rec_fget->doc = strdup(rec_fget->doc);
        |                               ^~~~~~
  /tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include/pybind11/pybind11.h:1284:31: note: (if you use ‘-fpermissive’, G++ will accept your code, but allowing the use of an undeclared name is deprecated)
  /tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include/pybind11/pybind11.h:1292:33: error: there are no arguments to ‘strdup’ that depend on a template parameter, so a declaration of ‘strdup’ must be available [-fpermissive]
   1292 |                 rec_fset->doc = strdup(rec_fset->doc);
        |                                 ^~~~~~
  /tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include/pybind11/pybind11.h: In instantiation of ‘pybind11::class_<type_, options>& pybind11::class_<type_, options>::def_property_static(const char*, const pybind11::cpp_function&, const pybind11::cpp_function&, const Extra& ...) [with Extra = {pybind11::is_method, pybind11::return_value_policy}; type_ = QPDFAnnotationObjectHelper; options = {}]’:
  /tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include/pybind11/pybind11.h:1263:80:   required from ‘pybind11::class_<type_, options>& pybind11::class_<type_, options>::def_property(const char*, const pybind11::cpp_function&, const pybind11::cpp_function&, const Extra& ...) [with Extra = {pybind11::return_value_policy}; type_ = QPDFAnnotationObjectHelper; options = {}]’
  /tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include/pybind11/pybind11.h:1252:91:   required from ‘pybind11::class_<type_, options>& pybind11::class_<type_, options>::def_property(const char*, const Getter&, const Setter&, const Extra& ...) [with Getter = pybind11::cpp_function; Setter = std::nullptr_t; Extra = {pybind11::return_value_policy}; type_ = QPDFAnnotationObjectHelper; options = {}]’
  /tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include/pybind11/pybind11.h:1234:58:   required from ‘pybind11::class_<type_, options>& pybind11::class_<type_, options>::def_property_readonly(const char*, const pybind11::cpp_function&, const Extra& ...) [with Extra = {pybind11::return_value_policy}; type_ = QPDFAnnotationObjectHelper; options = {}]’
  /tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include/pybind11/pybind11.h:1228:87:   required from ‘pybind11::class_<type_, options>& pybind11::class_<type_, options>::def_property_readonly(const char*, const Getter&, const Extra& ...) [with Getter = std::basic_string<char> (QPDFAnnotationObjectHelper::*)(); Extra = {}; type_ = QPDFAnnotationObjectHelper; options = {}]’
  src/qpdf/annotation.cpp:28:82:   required from here
  /tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include/pybind11/pybind11.h:1284:37: error: ‘strdup’ was not declared in this scope; did you mean ‘strcmp’?
   1284 |               rec_fget->doc = strdup(rec_fget->doc);
        |                               ~~~~~~^~~~~~~~~~~~~~~
        |                               strcmp
  /tmp/pip-build-env-fdjj5aaz/overlay/lib/python3.7/site-packages/pybind11/include/pybind11/pybind11.h:1292:39: error: ‘strdup’ was not declared in this scope; did you mean ‘strcmp’?
   1292 |                 rec_fset->doc = strdup(rec_fset->doc);
        |                                 ~~~~~~^~~~~~~~~~~~~~~
        |                                 strcmp
  error: command 'gcc' failed with exit status 1
  ----------------------------------------
  ERROR: Failed building wheel for pikepdf
Failed to build pikepdf
ERROR: Could not build wheels for pikepdf which use PEP 517 and cannot be installed directly

所以看起来 pybind11.h 需要 strdup() 但它不可用。 strdup() 在 /usr/include/string.h 中声明，其中包含这个：

#if __MISC_VISIBLE || __POSIX_VISIBLE >= 200809 || __XSI_VISIBLE >= 4
char    *strdup (const char *) __malloc_like __result_use_check;
#endif
char    *_strdup_r (struct _reent *, const char *);
#if __POSIX_VISIBLE >= 200809
char    *strndup (const char *, size_t) __malloc_like __result_use_check;
#endif

所以我尝试在命令行中添加显式 -D__MISC_VISIBLE 看看这是否能解决问题，但它不起作用（如上所示）。我捕获预处理器输出 -E 并发现即使使用 -D__MISC_VISIBLE 它的行为就好像没有定义该宏一样。只出现_strdup_r：

Preprocessor output snippet

# 86 "/usr/include/string.h" 3 4
char *_strdup_r (struct _reent *, const char *);

这就是我被困的地方。我似乎无法制作编译器包括 strdup()。我不确定下一步如何进行，欢迎任何建议。

Answer 1

strdup 是标准 C 的扩展。

Cygwin headers 比其他系统更严格范围报告于

/usr/include/sys/features.h

通常的解决方案：

将 -std=c++11 替换为 -std=gnu++11
完全删除 -std=xxx
使用-D_GNU_SOURCE

最后两个或多或少是等价的，因为默认范围是最大的， -std=xxx 减少它。

Cygwin 下的 gcc 9.3.0 预处理器：cmdline -Dname 但名称似乎未定义

gcc 9.3.0 preprocessor under Cygwin: cmdline -Dname but name seems to be undefined

c++

cygwin

preprocessor

strdup

pikepdf