1 /*------------------------------
2 func_ptr.c -- 使用函数指针
3 ------------------------------*/
4
5 #include <stdio.h>
6 #include <string.h>
7 #include <ctype.h>
8
9 #define LEN 81
10
11 char* s_gets(char *st, int n);
12 char showmenu(void);
13 void eatline(void); //读取至行末尾
14 void ToUpper(char*); //把字符串转换为大写
15 void ToLower(char*); //把字符串转换为小写
16 void Transpose(char*); //大小写转换
17 void Dummy(char*); //不更改字符串
18 void show(void (*fp)(char*), char *str);
19
20
21 int main()
22 {
23 char line[LEN], copy[LEN];
24 char choice;
25 void (*pfn)(char*); //声明函数指针
26
27 puts("Enter a string (empty line to quit):");
28
29 while (s_gets(line, LEN) != NULL && line[0] != '\0')
30 {
31 while ((choice = showmenu()) != '\n')
32 {
33 switch (choice)
34 {
35 case 'u': pfn = ToUpper; break;
36 case 'l': pfn = ToLower; break;
37 case 't': pfn = Transpose; break;
38 case 'o': pfn = Dummy; break;
39 }
40
41 strcpy(copy, line); //为 show() 函数拷贝一份
42 show(pfn, copy); //根据用户选择，使用选定的函数
43 }
44
45 puts("Enter a string (empty line to quit):");
46 }
47
48 puts("Bye!");
49
50 return 0;
51 }
52
53 char showmenu()
54 {
55 char ans;
56
57 puts("Enter menu choice:");
58 puts("u) uppercase 1) lowercase");
59 puts("t) transposed case o) original case");
60 puts("n) next string");
61
62 ans = tolower(fgetc(stdin)); //获取用户输入,转换为小写
63 eatline(); //清理输入行
64
65 while (strchr("ulton", ans) == NULL)
66 {
67 puts("Please enter a u, l, t, o, or n:");
68 ans = tolower(fgetc(stdin));
69 eatline();
70 }
71
72 return ans;
73 }
74
75 void eatline(void)
76 {
77 while (fgetc(stdin) != '\n') continue;
78 }
79
80 void ToUpper(char *str)
81 {
82 while (*str)
83 {
84 *str = toupper(*str);
85 ++str;
86 }
87 }
88
89 void ToLower(char *str)
90 {
91 while (*str)
92 {
93 *str = tolower(*str);
94 ++str;
95 }
96 }
97
98 void Transpose(char *str)
99 {
100 while (*str)
101 {
102 if (islower(*str))
103 *str = toupper(*str);
104 else if (isupper(*str))
105 *str = tolower(*str);
106
107 ++str;
108 }
109 }
110
111 void Dummy(char *str)
112 {
113 //do nothing
114 }
115
116 void show(void (*fp)(char*), char *str)
117 {
118 (*fp)(str); //把用户选定的函数作用于str
119 puts(str); //显示结果
120 }
121
122 char* s_gets(char *st, int n)
123 {
124 char *ret_val, *find;
125
126 if (ret_val = fgets(st, n, stdin))
127 {
128 if (find = strchr(st, '\n'))
129 *find = '\0';
130 else
131 while (fgetc(stdin) != '\n') continue;
132 }
133
134 return ret_val;
135 }
