Thread: Linked List Help

Hello Everyone,

I'll just jump right into it.

Code:

void searchLibrary(book *list)
{
    string key;
    string search;
    book *searchList = NULL;
    book *temp = NULL;
    book *found = NULL;
    int ctr = 0;
    int i = 0;
    int resp = 0;
    
    screenHeader("Search Function");


    cout << "                       Type out one of the options below." << endl << endl << endl << endl;


    cout << "\tHow would you like to search entries?" << endl << endl;
    cout << "\t\t- Author" << endl << endl;
    cout << "\t\t- Title" << endl << endl;
    cout << "\tSearch entires by: ";
    getline(cin, search);


    if(search.at(0) == 'a' || search.at(0) == 'A'){
        //search by author
        cout << endl << "\tEnter the author: ";
        getline(cin, key); // Key to look for when searching


        while(list){ // Search the whole array
            if(key == list->author){ // If a match
                if(ctr == 0){
                    found = new book;
                    found = list;
                    searchList = found;
                    found->next = NULL;
                    ctr++; // Counter for the number of results found
                }
                else{
                    temp = new book;
                    temp = list;
                    temp->next = NULL;
                    found->next = temp;
                    found = found->next;
                }
            }
            list = list->next;
        }
        if(ctr == 0) // If the counter equals zero, then no results were found
            cout << endl << endl << "                           ** No results were found **" << endl << endl << endl;
        else{ // Display the results
            system("cls");
            screenHeader("Search Results");
            cout << "\tResults Found: " << ctr << endl << endl;
            tableDisplay(searchList);
        }
        
        transitionScreen();
    }
    else if(search.at(0) == 't' || search.at(0) == 'T'){
        //search by title
        cout << endl << "\tEnter the title: ";
        getline(cin, key);


        while(list){ // Search the list
            if(key == list->title){ // If there is a match
                if(ctr == 0){
                    found = new book;
                    found = list; 
                    searchList = found;
                    found->next = NULL;
                    ctr++; // Counter for the number of results found
                }
                else{
                    temp = new book;
                    temp = list;
                    temp->next = NULL;
                    found->next = temp;
                    found = found->next;
                }
            }
            list = list->next;
        }
        if(ctr == 0) // If the counter equals zero, then no results were found
            cout << "                           ** No results were found **" << endl << endl << endl;
        else{ // Display the results
            system("cls");
            screenHeader("Search Results");
            cout << "\tResults Found: " << ctr << endl << endl;
            tableDisplay(searchList);
        }
        transitionScreen();
    }
    else{
        cout << "You did not enter one of the following options." << endl << endl << endl;
        transitionScreen();
    }
    
}

Code:

searchLibrary(orderList);

orderList is the head of a list I'm passing to the search function. The problem is in the search function, when found->next = NULL executes, list->next also updates to equal NULL, which means I can no longer continue to search list.

Thanks for your help!

The problem is in the search function, when found->next = NULL executes, list->next also updates to equal NULL, which means I can no longer continue to search list.

I didn't really look at your code but if you are only doing one assignment, this means that found and list have the same value which is something you don't want. So make sure found and list don't have the same value because the only way that assigning the value of next to null affects another pointer is if those pointers both point to the same thing.

Just like this :

Code:

                    found = new book; // you request a heap allocation
                    found = list; // you immediately overwrite the location of the allocation with a previously existing one

Ok so I understand what you're saying. How do I make them not point to the same thing? Do I send the address of the original list or a copy of it?
Thanks!

Sorry this is a late reply but I'm going to answer your question with another question, what do you want "found" to do? What is it? What's its purpose in the program? Answering these will definitely help you answer the question you asked.

I'm searching "list" and if there is a match I want "found" to copy of the node from "list". Then I would add "found" to "searchList", which is a list of all matches. Hopefully this answers your question. Also sorry for the late reply

Thank you so much!!!