Remove Items from a struct array-CodePudding

So I'm implementing a TCP server chatroom in C and using poll to handle multiple clients. Users register with a username and password and then Login with it. When they login I want to add them to this struct array.

struct onlineUsers{
int sockfd;
char username[9]; //usernames size is maximum 8 characters
};

struct onlineUsers users[10];

//The login function is pretty long so is here the relevant part.
    if(!searchExist(search, db)){
        printf("Account doesnt exist.\n");
        fclose(db);
        free(search);
        return -1;
    }
    else{
        printf("Logged in\n");
        // Add to onlineUser struct arr[]
    }

But when the client closes the connection how would you remove that specific element from the onlineUsers array? I haven't implemented the way to add them since I don't really have a good way to remove them.

CodePudding user response：

I reworked this into a minimal example and implemented a linear search for you (use lfind in remove_user() and lsearch in add_user() if available):

#include <assert.h>
#include <string.h>

#define MAX_NAME 8
#define MAX_USERS 2

struct user {
    char name[MAX_NAME   1];
};

unsigned find_pos(struct user *users, const char *name) {
    unsigned empty = MAX_USERS;
    for(unsigned i = 0; i < MAX_USERS; i  ) {
       if(empty == MAX_USERS && !users[i].name[0]) empty = i;
       if(!strcmp(users[i].name, name)) return i;
    }
    return empty;
}

int add_user(struct user *users, const char *name) {
    unsigned pos = find_pos(users, name);
    if(pos == MAX_USERS) return -1;
    if(users[pos].name[0]) return 1;
    // safe as name[8] is 0 initialized; otherwise
    // copy MAX_NAME   1 then set name[MAX_NAME] = '\0'
    // to ensure string is \0 terminated.
    strncpy(users[pos].name, name, MAX_NAME);
    return 0;
}

int remove_user(struct user *users, const char *name) {
    int pos = find_pos(users, name);
    if(!users[pos].name[0] || strcmp(users[pos].name, name)) return 1;
    users[pos].name[0] = '\0';
    return 0;
}


int main() {
    struct user users[MAX_USERS] = { 0 };
    assert(add_user(users, "bob") == 0); // ok (1 of 2)
    assert(add_user(users, "bob") == 1); // duplicate
    assert(remove_user(users, "bob") == 0); // ok (empty)
    assert(remove_user(users, "jane") == 1); // non-existing
    assert(add_user(users, "bob") == 0); // ok (1 of 2)
    assert(add_user(users, "jane") == 0); // ok (2 of 2)
    assert(add_user(users, "jack") == -1); // full
    assert(remove_user(users, "bob") == 0); // ok
    assert(find_pos(users, "jane") == 1); // ok (not empty slot)
}