Passing an array of strings without having contents modified - c

Question

I have been trying to pass an array of strings into a function that finds all of the IP addresses of the host. My problem is immediately after I fill the array up with the addresses the contents are changed unexpectedly. I print the contents of the array immediately after I assign a string to one part of the array, this is how I know I am initializing the array. Then after the loop is done I try accessing all of the addresses in the array and all of the values are changed to the value I last passed into the array. Why is this? What am I doing wrong?
Here is the function:
static int getHostIP(char*ip_list[])
{
char hostName[80];
if(gethostname(hostName, sizeof(hostName)) == SOCKET_ERROR)
{
printf("Error %s when getting host name.\n", WSAGetLastError());
return 1;
}
printf("Hostname: %s\n", hostName);
struct addrinfo *result = NULL;
if(getaddrinfo(hostName,NULL, NULL, &result) == 1)
{
printf("Error %s when getting host address info.\n", WSAGetLastError());
return 1;
}
//iterate over IP addresses
struct addrinfo *ptr;
int x = 0;
for(x = 0,ptr = result; ptr != NULL;ptr = ptr->ai_next, x++)
{
struct sockaddr_in *hostaddr = (struct sockaddr_in*)ptr->ai_addr;
char ip_addr[80];
inet_ntop(ptr->ai_family,(void*)&hostaddr->sin_addr, ip_addr, sizeof(ip_addr));
ip_list[x] = ip_addr;
}
int i;
for(i = 0; i < 7;i++)
{
printf("IP: %s\n", ip_list[i]);
}
return 0;
}
EDIT
Calling code:
char * ip_list[80] = {0};
//TODO: Get Host IP address
if(getHostIP(ip_list) == 1) return 1;

Answer 1

The behaviour you are experiencing is caused by the variable ip_addr which is always pointing to the same buffer in the stack during each iteration. Thus, all pointers in ip_list are pointing to the same buffer which contains the value calculated in the last iteration of the loop.
If you allocate this buffer in the heap by using malloc the problem should be solved because,now the loop block will create a new buffer for each ip. For example :
#define BUFFER_SIZE 80 // no in the function body
char * ip_addr = NULL;
for(x = 0,ptr = result; ptr != NULL;ptr = ptr->ai_next, x++)
{
ip_addr = malloc(BUFFER_SIZE);
struct sockaddr_in *hostaddr = (struct sockaddr_in*)ptr->ai_addr;
inet_ntop(ptr->ai_family,(void*)&hostaddr->sin_addr, ip_addr, BUFFER_SIZE);
ip_list[x] = ip_addr;
}

Answer 2

How is your data allocated ?
Try with:
static int getHostIP(char**ip_list)

Answer 3

Are you properly initializing the array you are passing in to this function. You are declaring an input of an array of char pointers. When ever you pass an array in c you must also pass along the length the array was initialized with. The memory needs to live somewhere and be reserved by the system.
Can you please provide the calling code so we can see what you are doing wrong.
Alternatively --- you could pass this entire array byref so you would just be getting an out pointer and the array would be declared by this function. Since you have no idea how many IP addresses you might match that might be a superior design.