Conflict of types in function

Question

I’m trying to create a list structure using struct.

Only when compiling my code, I get an error because even specifying the type Lista, he’s in some kind of trouble.

Follow the full code:

#include <stdio.h>
#include <conio.h>

struct lista {
    int info;
    struct lista* prox;
};

typedef struct lista Lista;

int main(void)
{
    Lista* l; 
    l = list_new();
    l = list_add(l, 23);
    l = list_add(l, 45);
    list_print ( l ); 
    
    return(0);
}

Lista* list_new (void)
{
    return NULL;
}

Lista* list_add (Lista* l, int i)
{
    Lista* novo = (Lista*) malloc(sizeof(Lista));
    novo -> info = i;
    novo -> prox = l;
    return novo;
}

void list_print (Lista* l)
{
    do {
        printf(“%d\t”,l->info);
        l = l->prox;
    } while (l != NULL); 
}

The error is giving on line 22:

[Error] Conflicting types for 'list_new':

List* list_new (void)

Answer 1

I put on the ideone. And in the repl it.. Also put on the Github for future reference. And after solving a number of other problems not listed in the question the code compiled and ran perfectly.

If you want to make it more explicit and maybe meet some compiler requirement you’re using, do a cast type returned to match the return type. So:

#include <stdio.h>
#include <stdlib.h>

struct lista {
    int info;
    struct lista* prox;
};

typedef struct lista Lista;

Lista* list_new(void) {
    return (Lista*)NULL;
}

Lista* list_add(Lista* l, int i) {
    Lista* novo = malloc(sizeof(Lista));
    novo -> info = i;
    novo -> prox = l;
    return novo;
}

void list_print(Lista* l) {
    do {
        printf("%d\t",l->info);
        l = l->prox;
    } while (l != NULL); 
}

int main(void) {
    Lista* l = list_new();
    l = list_add(l, 23);
    l = list_add(l, 45);
    list_print(l); 
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.

Answer 2

Simple, you say the function list_new returns of type Lista and then it’s returning NULL:

Lista* list_new (void)
{
    return NULL;
}