Array of Structs strange output? - c

Question

Can anyone give me some indication as to why array of structs doesn't print out properly ?
I think its something to do with the memory I have allocated to the struct I am unsure !!
Using mac osx mountain lion xcode 4 gcc
Thanks for any help completely stuck!!
(Please have patience I am only a student !)
#include <stdio.h>
#include <limits.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
typedef struct{
char* one;
char* two;
} Node;
Node *nodes;
int count = 0;
//-----------------------------------------------------------------------
void add(char *one,char*two){
char x[40];
char y[40];
printf("reached..\n");
strcpy(x,one);
strcpy(y,two);
printf("--> X: %s\n",x);
printf("--> Y: %s\n",y);
Node newNode;
newNode.one = x;
newNode.two = y;
nodes[count]= newNode;
count++;
}
//-----------------------------------------------------------------------
//-----------------------------------------------------------------------
void print(){
int x;
for (x = 0; x < 10; x++)
{
printf("%d : (%s, %s) \n",x,nodes[x].one, nodes[x].two);
}
}
//-----------------------------------------------------------------------
//-----------------------------------------------------------------------
void check(char **arg)
{
if(strcmp(*arg, "Add") == 0)
{
add(arg[1],arg[2]);
}else if(strcmp(*arg,"print") == 0)
{
print();
}else{
printf("Error syntax Enter either: \n Add [item1][item2]\n OR \n print\n");
}
}
//-----------------------------------------------------------------------
void readandParseInput(char *line,char **arg)
{
if (fgets (line, 512, stdin)!= NULL) {
char * pch;
pch = strtok (line," \n\t");
int count = 0;
arg[0] = pch;
while (pch != NULL)
{
count++;
pch = strtok (NULL, " \n\t");
arg[count] =pch;
}
}else{
printf("\n");
exit(0);
}
}
//-----------------------------------------------------------------------
int main()
{
int size = 100;
nodes = calloc(size, sizeof(Node));
int i;
for(i = 0;i <100; i++){
printf("%s , %s \n",nodes[i].one,nodes[i].two );
// nodes[i].one = ".";
// nodes[i].two = ".";
}
char line[512]; /* the input line */
char *arg[50]; /* the command line argument */
while (1)
{
readandParseInput(line,arg);
if(arg[0] != NULL){
check(arg);
}
}
return(0);
}

Answer 1

You're keeping pointers to the following automatic variables:
char x[40];
char y[40];
These go out of scope when add() returns, leaving you with dangling pointers.
You either have to turn Node::one and Node::two into arrays, or allocate memory for them on the heap.

Answer 2

In you add() function, you cannot assign one struct to another via an = operator... you would have to copy it...
memcpy( &nodes[count], &newNode )

Answer 3

#include <stdio.h>
#include <stdlib.h>
typedef struct {
char *fn;
}NAME;
#define NAME_LEN 20
int main()
{
NAME name;
name.fn = (char *) calloc(NAME_LEN, sizeof(char));
strcpy(name.fn, "Namco");
printf("Name: %s\n", name.fn);
free(name.fn);
return 0;
}
you can't just assign a string like this in c
newNode.one = x;
newNode.two = y;
what is newNode.one referring to???

Answer 4

at Function add
newNode.one = x;
newNode.two = y;
to
newNode.one = strdup(x);
newNode.two = strdup(y);