#define宏定义

dt3tc

我知道#define是宏定义指令，但这个代码中的“#define Py_ASDL_H”语句不像啊（宏名后无字符串），请问这句是什么意思

1. #ifndef Py_ASDL_H
   
2. #define Py_ASDL_H
   
3. 
   
4. typedef PyObject * identifier;
   
5. typedef PyObject * string;
   
6. typedef PyObject * object;
   
7. 
   
8. /* It would be nice if the code generated by asdl_c.py was completely
   
9.    independent of Python, but it is a goal the requires too much work
   
10.    at this stage.  So, for example, I'll represent identifiers as
    
11.    interned Python strings.
    
12. */
    
13. 
    
14. /* XXX A sequence should be typed so that its use can be typechecked. */
    
15. 
    
16. typedef struct {
    
17.     int size;
    
18.     void *elements[1];
    
19. } asdl_seq;
    
20. 
    
21. typedef struct {
    
22.     int size;
    
23.     int elements[1];
    
24. } asdl_int_seq;
    
25. 
    
26. asdl_seq *asdl_seq_new(int size, PyArena *arena);
    
27. asdl_int_seq *asdl_int_seq_new(int size, PyArena *arena);
    
28. 
    
29. #define asdl_seq_GET(S, I) (S)->elements[(I)]
    
30. #define asdl_seq_LEN(S) ((S) == NULL ? 0 : (S)->size)
    
31. #ifdef Py_DEBUG
    
32. #define asdl_seq_SET(S, I, V) { \
    
33.         int _asdl_i = (I); \
    
34.         assert((S) && _asdl_i < (S)->size); \
    
35.         (S)->elements[_asdl_i] = (V); \
    
36. }
    
37. #else
    
38. #define asdl_seq_SET(S, I, V) (S)->elements[I] = (V)
    
39. #endif
    
40. 
    
41. #endif /* !Py_ASDL_H */
    

复制代码

from python 3.1.3\include\asdl.h

仰望天上的光

#define Py_ASDL_H
就是把Py_ASDL_H
定义为什么都没有，这里兵不是为了把Py_ASDL_H定义成什么特殊的东西，主要是为了#ifndef检测是否定义过Py_ASDL_H