1 /*------------------------------  2     func_ptr.c -- 使用函数指针  3 ------------------------------*/  4   5 #include 
      
         6 #include 
       
          7 #include 
        
           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 nothing114 }115 116 void show(void (*fp)(char*), char *str)117 {118     (*fp)(str);        //把用户选定的函数作用于str119     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         else131             while (fgetc(stdin) != '\n') continue;132     }133 134     return ret_val;135 }