C 语言复杂声明

对C复杂声明的理解，到现在还是不行，这是从K&R 第二版中找到的一个程序， 可以加强理解：

dcl.h

 

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <ctype.h>
 4 
 5 #define MAXTOKEN 100
 6 #define BUFSIZE 100
 7 
 8 enum { NAME, PARENS, BRACKETS };
 9 
10 char buf[BUFSIZE];
11 int bufp = 0;
12 int getch(void);
13 void ungetch(int c);
14 
15 int tokentype;
16 char token[MAXTOKEN];
17 char name[MAXTOKEN];
18 char datatype[MAXTOKEN];
19 char out[1000];
20 
21 void dcl(void);
22 void dirdcl(void);
23 int gettoken(void);

 

dcl.c

 

 1 #include "dcl.h"
 2 
 3 void dcl(void)
 4 {
 5     int ns;
 6 
 7     for(ns = 0; gettoken() == '*'; )
 8         ns++;
 9     dirdcl();
10     while(ns-- > 0)
11         strcat(out, " pointer to");
12 }
13 
14 void dirdcl(void)
15 {
16     int type;
17     
18     if( tokentype == '(') {
19         dcl();
20         if(tokentype != ')')
21             printf("error: missing )\n");
22     } else if (tokentype == NAME) {
23         strcpy(name, token);
24     } else {
25         printf("error: expected name or (dcl)\n");
26     }
27     while((type = gettoken()) ==  PARENS || type == BRACKETS)
28         if(type == PARENS) {
29             strcat(out, " function returning");
30         } else {
31             strcat(out, " array");
32             strcat(out, token);
33             strcat(out, " of");
34         }
35 }
36 
37 int gettoken(void)
38 {
39     int c;
40     char *p = token;
41 
42     while((c = getch()) == ' ' || c == '\t')
43         ;
44     if(c == '(') {
45         if((c = getch()) == ')') {
46             strcpy(token, "()");
47             return tokentype = PARENS;
48         } else {
49             ungetch(c);
50             return tokentype = '(';
51         }
52     } else if (c == '[') {
53         for(*p++ = c; (*p++ = getch()) != ']';  )
54             ;
55         *p = '\0';
56         return tokentype = BRACKETS;
57     } else if(isalpha(c)) {
58         for(*p++ = c; isalpha(c = getch()); )
59             *p++ = c;
60         *p = '\0';
61         ungetch(c);
62         return tokentype = NAME;
63     } else
64         return tokentype = c;
65 }
66 
67 int getch(void)
68 {
69     return (bufp > 0) ? buf[--bufp] : getchar();
70 }
71 void ungetch(int c)
72 {
73     if(bufp >= BUFSIZE)
74         printf("ungetch: too many characters\n");
75     else
76         buf[bufp++] = c;
77 }
78 
79 int main(void) 
80 {
81     while(gettoken() != EOF) {
82         strcpy(datatype, token);
83         out[0] = '\0';
84         dcl();
85         if(tokentype != '\n')
86             printf("syntax error\n");
87         printf("%s: %s %s\n", name, out, datatype);
88     }
89     return 0;
90 }