本文深入探讨了Python源代码中针对不同情况定义宏的机制，解释了为何需要在宏定义中使用未定义变量，并阐述了这种机制如何在库文件中实现方法名称的有条件导出。
a usage of c macro-小雨-iteye技术网站
2011年08月01日
For some reason, I need to understand the following code. Header File # include/unicodeobject.h from python source code #ifndef Py_UNICODE_WIDE // other code # define PyUnicode_Decode PyUnicodeUCS2_Decode // other code #else // other code # define PyUnicode_Decode PyUnicodeUCS4_Decode // other code #endif
Source File # Objects/unicodeobject.c // other code PyObject *PyUnicode_Decode(const char *s, Py_ssize_t size, const char *encoding, const char *errors) { // other code } // other code
At first sight, I am confused. Why to define a macro against some thing undefined such as Unicode_Decode PyUnicodeUCS2_Decode and PyUnicodeUCS4_Decode? After some thinking, I find that this macro is used to export method names conditionally in the library created for these source files. If Py_UNICODE_WIDE is undefined, PyUnicodeUCS2_Decode is exported. Otherwise, PyUnicodeUCS4_Decode is exported. There is no a method called Unicode_Decode since it will be replaced after preprocessing.
2011年08月01日
For some reason, I need to understand the following code. Header File # include/unicodeobject.h from python source code #ifndef Py_UNICODE_WIDE // other code # define PyUnicode_Decode PyUnicodeUCS2_Decode // other code #else // other code # define PyUnicode_Decode PyUnicodeUCS4_Decode // other code #endif
Source File # Objects/unicodeobject.c // other code PyObject *PyUnicode_Decode(const char *s, Py_ssize_t size, const char *encoding, const char *errors) { // other code } // other code
At first sight, I am confused. Why to define a macro against some thing undefined such as Unicode_Decode PyUnicodeUCS2_Decode and PyUnicodeUCS4_Decode? After some thinking, I find that this macro is used to export method names conditionally in the library created for these source files. If Py_UNICODE_WIDE is undefined, PyUnicodeUCS2_Decode is exported. Otherwise, PyUnicodeUCS4_Decode is exported. There is no a method called Unicode_Decode since it will be replaced after preprocessing.
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