Question

Is there a better way to maintain a list of strings in C besides using typedef char* and declaring an array of type string? I am trying to manage a list of member names that join the group via socket program. But every time a new member joins the group – old member names get overridden. Part of the sample code is like this:

typedef char * string;
string  List[10];

and new member joins like this:

List[index]=membername;

Thanks.

Answer 1

You’re probably (not enough context) not allocating the strings properly.

string List[10];

only allocates an array of 10 string, i.e. 10 char *, i.e. 10 character pointers. It doesn’t allocate any storage for the strings themselves.

So if your membername above is e.g. a global char * that you’re copying data from the network to, all your slots in List will end up pointing to that very same memory location.

To make it work, you’d need to allocate (and carefully free) all the slots in List. Something like:

List[index] = strdup(membername);

For better chances of catching errors early, initially set your List to all null pointers.

for (int i=0; i<10; i++) List[i] = NULL;

and when a user “goes away”, free and reset that slot to NULL:

free(List[index]);
List[index] = NULL;

That way you’ll get nice, nasty segfaults if you don’t manage your slots carefully enough 🙂