CS 1723, Practice with structs, Wed Aug 20 1998, Page 1 of 2runner% cat structs.c/* structs.c: study the struct in C *//* Written 4 Mar 1997 by NR Wagner */#include <stdio.h>#include <stdlib.h>#include <string.h>struct a_tag { char c; int i; char *w;};void print_a(int test_num, struct a_tag a);void print_p(int test_num, struct a_tag *p);struct a_tag return_struct(void);struct a_tag *return_ptr(void);struct a_tag *return_bad(void);int main(){ struct a_tag a1, a2, a3; /* structs */ struct a_tag *p1 = &a1; /* p1 points to a1 */ struct a_tag *p3, *p4; /* pointers */ /* initialize a1 */ a1.c = ’X’; a1.i = 99; a1.w = (char *) malloc(20); strcpy(a1.w, "Now is the time"); /* printing related to a1, using p1 also */ /* shows that print_a copies struct, while */ /* print_p copies a pointer to the struct */ print_a(1, a1); print_p(2, p1); print_a(3, a1); print_p(4, p1); /* = copies struct on right into struct on left */ a2 = a1; print_a(5, a2); /* change a1 and a2 gets changed also! */ strcpy(a1.w, "Quick brown foxes"); print_a(6, a2); /* try out returns, first returning a struct */ a3 = return_struct(); print_a(7, a3); /* then try returning a pointer to a struct */ p3 = return_ptr(); print_p(8, p3); /* finally return a pointer to local auto storage */ p4 = return_bad(); print_p(9, p4); return 0;}/* print_a: print a struct passed by value (copied) */void print_a(int test_num, struct a_tag a){ printf("Test %i, ", test_num); printf("Passing struct, fields: c:%c, i:%3i, w:\"%s\"\n", a.c, a.i, a.w); /* increment below has no effect back in main */ a.i++; /* same as (a.i)++ */}CS 1723, Practice with structs, Wed Aug 20 1998, Page 2 of 2/* print_a: print a struct where pointer is passed */void print_p(int test_num, struct a_tag *p){ printf("Test %i, ", test_num); printf("Passing pointer, fields: c:%c, i:%3i, w:\"%s\"\n", (*p).c, p -> i, p -> w); /* (*p).c same as p -> c */ /* increment below changes struct back in main */ p->i++; /* same as (p->i)++ */}/* return_struct: return a struct by value (copied) */struct a_tag return_struct(void){ struct a_tag a; a.c = ’Y’; a.i = 88; a.w = "My dog has fleas"; /* can return local auto storage, because it is copied */ return a;}/* return_ptr: return a pointer to a struct */struct a_tag *return_ptr(void){ struct a_tag *p; p = (struct a_tag *) malloc(sizeof(struct a_tag)); p -> c = ’Z’; (*p).i = 77; /* same as p -> i = 77 */ p -> w = "Yours does too"; return p;}/* return_bad: return local auto storage through *//* a pointer to a struct--a serious error! */struct a_tag *return_bad(void){ struct a_tag *p; struct a_tag a; p = &a; p -> c = ’U’; (*p).i = 666; /* same as p -> i = 66 */ p -> w = "Should screw up"; return p;}runner% lint -m -u structs.cfunction returns value which is always ignored printf strcpy runner% cc -o structs structs.crunner% structsTest 1, Passing struct, fields: c:X, i: 99, w:"Now is the time"Test 2, Passing pointer, fields: c:X, i: 99, w:"Now is the time"Test 3, Passing struct, fields: c:X, i:100, w:"Now is the time"Test 4, Passing pointer, fields: c:X, i:100, w:"Now is the time"Test 5, Passing struct, fields: c:X, i:101, w:"Now is the time"Test 6, Passing struct, fields: c:X, i:101, w:"Quick brown foxes"Test 7, Passing struct, fields: c:Y, i: 88, w:"My dog has fleas"Test 8, Passing pointer, fields: c:Z, i: 77, w:"Yours does too"Test 9, Passing pointer, fields: c:õ, i: 85, w:"õþp"runner% CC -o structscc structs.crunner% structscc (same output)runner% gcc -o structsgcc structs.crunner% structsgcc. . .Test 9, Passing pointer, fields: c:, i:68608,