I'm a total beginner to C (obviously), and I thought functions initA and initB were interchangeable, since they both return a pointer to an object of type List (a custom struct) but only initA produces the expected output.
How is initA different from initB ?
List *initA() {
List *list = malloc(sizeof(*list));
Element *element = malloc(sizeof(*element));
element->number = 0;
element->next = NULL;
list->first = element;
return list;
}
List *initB() {
Element _el = {.number=0, .next=NULL};
Element *el = &_el;
List _list = {.first=el};
List *list = &_list;
return list;
}
Here is the full source code (trying to reproduce the first steps of a Linked List here, for pedagogic reasons)
#include <stdio.h>
#include <stdlib.h>
typedef struct Element Element;
struct Element {
int number;
Element *next;
};
typedef struct List List;
struct List {
Element *first;
};
List *initA() {
List *list = malloc(sizeof(*list));
Element *element = malloc(sizeof(*element));
element->number = 0;
element->next = NULL;
list->first = element;
return list;
}
List *initB() {
Element _el = {.number=0, .next=NULL};
Element *el = &_el;
List _list = {.first=el};
List *list = &_list;
return list;
}
void printList(List *list){
Element *el = list->first;
while (NULL != el) {
printf("number: %d, next: %p\n", el->number, el->next);
el = el->next;
}
}
int main(int argc, char *argv[]) {
/**
* output:
* number: 0, next: 0x0
*/
// List *list = initA();
/**
* output:
* number: 1344951776, next: 0x7fff502a55d0
* number: 1344951776, next: 0x29502a55e0
*/
List *list = initB();
printList(list);
return 0;
}
