Question

I read from file store the data into a list;

I want to add to the front of the list as I read in.

The insertion seems to work, but my print function causes a -1 return.
This is my code:

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

This is my list

typedef struct node{
int x,y,v;
struct node* next;
}node;

This is my insert:

node* insert(node* L, int x, int y, int v){
node* new= (node*)malloc(sizeof(node*));
new->x = x;
new->y = y;
new->v = v;
new->next=NULL;
if(L==NULL){
    L=new;
}
else{
new->next=L;
L=new;
}   
return L;
}

The problem seems to be here:

void printList(node* L){
node* c=NULL;
c=L;
while(c != NULL){
printf("x=%d, y=%d, v=%d\n", c->x, c->y, c->v);
c=c->next;
}
}

The main:

int main(int argc, char* argv[]){
FILE* in;
int h, w;
int x, y, v;
in = fopen(argv[1], "r");
if(in == NULL )
     {
           puts ( "cannot open file" ) ;
           exit(0) ;
     }
fscanf (in, "%d,%d\n", &h, &w);
printf("%d,%d\n", h, w);
node* L=NULL;
while( !feof (in) ){
    fscanf (in, "%d,%d,%d\n", &x, &y, &v);
    L=insert(L, x, y, v);
    //printf("x=%d, y=%d, v=%d\n", L->x, L->y, L->v);
    //printf("%d,%d,%d\n", x, y, v);
}

printList(L);
return 0;
}

What’s wrong, please?

Answer 1

node* new= (node*)malloc(sizeof(node*));

You’re allocating size for a pointer to node (4 bytes on a 32bit machine), but what you want is a node (16 bytes, or sizeof(node)).

Also, I’d say that even if C doesn’t care, I’d avoid new as a variable name. It is a keyword in many languages,