C examples for Pointer:Function Pointer
Uses function pointers
#include <stdio.h> #include <string.h> #include <ctype.h> #define LEN 81/*from w w w . j a v a 2 s .com*/ char * s_gets(char * st, int n); char showmenu(void); void eatline(void); // read through end of line void show(void (* fp)(char *), char * str); void ToUpper(char *); void ToLower(char *); void Transpose(char *); // transpose cases void Dummy(char *); // leave string unaltered int main(void) { char line[LEN]; char copy[LEN]; char choice; void (*pfun)(char *); // points a function having a // char * argument and no // return value puts("Enter a string (empty line to quit):"); while (s_gets(line, LEN) != NULL && line[0] != '\0') { while ((choice = showmenu()) != 'n') { switch (choice ) // switch sets pointer { case 'u' : pfun = ToUpper; break; case 'l' : pfun = ToLower; break; case 't' : pfun = Transpose; break; case 'o' : pfun = Dummy; break; } strcpy(copy, line);// make copy for show() show(pfun, copy); // use selected function } puts("Enter a string (empty line to quit):"); } puts("Bye!"); return 0; } char showmenu(void) { char ans; puts("Enter menu choice:"); puts("u) uppercase l) lowercase"); puts("t) transposed case o) original case"); puts("n) next string"); ans = getchar(); // get response ans = tolower(ans); // convert to lowercase eatline(); // dispose of rest of line while (strchr("ulton", ans) == NULL) { puts("Please enter a u, l, t, o, or n:"); ans = tolower(getchar()); eatline(); } return ans; } void eatline(void) { while (getchar() != '\n') continue; } void ToUpper(char * str) { while (*str) { *str = toupper(*str); str++; } } void ToLower(char * str) { while (*str) { *str = tolower(*str); str++; } } void Transpose(char * str) { while (*str) { if (islower(*str)) *str = toupper(*str); else if (isupper(*str)) *str = tolower(*str); str++; } } void Dummy(char * str) { printf("do nothing"); } void show(void (* fp)(char *), char * str) { (*fp)(str); // apply chosen function to str puts(str); // display result } char * s_gets(char * st, int n) { char * ret_val; char * find; ret_val = fgets(st, n, stdin); if (ret_val) { find = strchr(st, '\n'); // look for newline if (find) // if the address is not NULL, *find = '\0'; // place a null character there else while (getchar() != '\n') continue; // dispose of rest of line } return ret_val; }