Linked List problem..

Dear guys,

I'm facing some problem about the Name is not displaying as I expected..

Code:

---

#include <stdio.h>
#include <conio.h>
#include <stdlib.h>


int selection = 0; //Always return 0 after a function is executed


struct productInfo
{
    int categoryID;
    char categoryName[50];
    int productID;
    char productName[50];
    float productPrice;
    int productUnit;
    struct productInfo *nextPtr;
};


struct productInfo get;
struct productInfo *tempStorage;
struct productInfo *previousPtr = NULL;


void mainMenu (void);
void addItem (void);
void deleteItem (void);
void updateItem (void);
void sortItem (void);
void display (void);


/*In this problem, you will need to create an inventory system
that enable user to add, delete,
update product category (example: id, name)
product info (example: id, name, price, inventory level etc).*/


int main()
{
    do
    {
    mainMenu(); //Pick an option
    } while (selection == 0);
}


void mainMenu (void)
{
    printf("~*~*~*~Welcome to the main menu~*~*~*~\n"
    " 1 to add a category or item\n"
    " 2 to update a category or item\n"
    " 3 to delete an category or item\n"
    " 4 to end\n"
    "?");
    scanf("%d", &selection);


    switch(selection)
    {
        case 1:
            addItem();
            //sortItem();
            //system("CLS");
            display();
            break;
        case 2:
            deleteItem();
            break;
        case 3:
            updateItem();
            break;
        default:
            printf("Re-enter");
            selection = 0;
    }
}


void addItem (void)
{
    int tempCategoryID = 0;
    int tempProductID = 0;


    char tempCategoryName[50];
    char tempProductName[50];


    float tempProductPrice = 0.00;
    int tempProductUnit = 0;
   
    int decision = 0;
   
    fflush(stdin); //make sure all the buffered output is flushed
    printf("Please key in the Category ID :\n");
    scanf("%d", &tempCategoryID);
   
    fflush(stdin);
    printf("Please key in the Category Name :\n");
    scanf("%[^\n]", tempCategoryName);
   
    fflush(stdin);
    printf("Key in 1 if you have a product to store.\nKey in others number to skip.\n");
    scanf("%d", &decision);
   
    if (decision == 1) {
        fflush(stdin);
        printf("Please key in the Product ID :\n");
        scanf("&d", &tempProductID);
       
        fflush(stdin);
        printf("Please key in the Product Name :\n");
        scanf("%[^\n]", tempProductName);
       
        fflush(stdin);
        printf("Please key in the Product Price :\nRM");
        scanf("%f", &tempProductPrice);
       
        fflush(stdin);
        printf("Please key in the Product Unit :\n");
        scanf("%d", &tempProductUnit);
    } else {
        tempProductID = tempCategoryID*100;
        tempProductName[0] = '\0';
        tempProductPrice = 0.00;
        tempProductUnit = 0;
    }


    tempStorage = malloc(sizeof(struct productInfo));


    tempStorage -> categoryID = tempCategoryID;
    tempStorage -> categoryName[50] = tempCategoryName[50];
    tempStorage -> productID = tempProductID;
    tempStorage -> productName[50] = tempProductName[50];
    tempStorage -> productPrice = tempProductPrice;
    tempStorage -> productUnit = tempProductUnit;
    tempStorage -> nextPtr = previousPtr;
    previousPtr = tempStorage;
}


void display (void)
{
        struct productInfo *displayItem;
        displayItem = previousPtr;
        char checkName[50] = "";


        while (displayItem != NULL)
        {
                if (displayItem -> categoryName == checkName)
                {
                        printf("IDa : %d\n", displayItem -> productID);
                        printf("Name : %s\n", displayItem -> productName);
                        printf("Price : %.2f\n", displayItem -> productPrice);
                        printf("Unit : %d\n", displayItem -> productUnit);
                } else {
                        printf("Category\n");
                        printf("IDb : %d\n", displayItem -> categoryID);
                        printf("Name : %s\n", displayItem -> categoryName); //no output
                        checkName[50] = displayItem -> categoryName[50];
                        printf("Product\n");


                        if (displayItem -> productName == "")
                        {
                                printf("No product");
                        } else {
                                printf("IDc : %d\n", displayItem -> productID); //output have problem
                                printf("Name : %s\n", displayItem -> productName); //no output
                                printf("Price : %.2f\n", displayItem -> productPrice);
                                printf("Unit : %d\n", displayItem -> productUnit);
                        }
                }
                displayItem = displayItem -> nextPtr;
        }
}


void deleteItem (void)
{
    printf("asdads\n");
}


void updateItem (void)
{
    printf("asdads\n");
}

---

I found that, all about char has no output, why :(

Regards,
Milo.

Hi,

Looking at your code, what I understand is that at the line n° 155 you test equality based on address of pointers and not their pointed values

Code:

---

if (displayItem -> categoryName == checkName)
{
    printf("IDa : %d\n", displayItem -> productID);
    printf("Name : %s\n", displayItem -> productName);
    printf("Price : %.2f\n", displayItem -> productPrice);
    printf("Unit : %d\n", displayItem -> productUnit);
}
else
{
    printf("Category\n");
    printf("IDb : %d\n", displayItem -> categoryID);
    printf("Name : %s\n", displayItem -> categoryName); //in here, the name simply does not come out.. why?
}

---

So if the program flow is directed towards the else block, this means that:

Code:

---

displayItem -> categoryName != checkName

---

Which is obviously true as they are two different pointers pointing to two different places, Before the while loop at the line 153 you declare checkName as the following

Code:

---

char checkName[50] = "";

---

This will always lead you to the Else block with checkName as empty.

Regards,
Dariyoosh

Hellow :) thanks for your respond,
I believe the problem is not there, I think the problem is somewhere around :

Code:

---

        tempStorage -> categoryID = tempCategoryID;
        tempStorage -> categoryName[50] = tempCategoryName[50]; //this part
        tempStorage -> productID = tempProductID;
        tempStorage -> productName[50] = tempProductName[50]; //this part
        tempStorage -> productPrice = tempProductPrice;
        tempStorage -> productUnit = tempProductUnit;
        tempStorage -> nextPtr = previousPtr;
        previousPtr = tempStorage;

---

I did something wrong around here, thus making the string not passed.. sigh i'm still very confusing..

I have never seen an assignment like this

Code:

---

tempStorage -> productName[50] = tempProductName[50]; //this part

---

Are you sure that you compile this without any error? (Linux or Windows?)

I get a couple errors when I compile your code:

Code:

---

$ make list
gcc -Wall -Werror -ggdb3 -std=c99 -pedantic list.c -o list -lm -lpthread -lefence
list.c: In function ‘addItem’:
list.c:111:9: error: too many arguments for format [-Werror=format-extra-args]
list.c: In function ‘display’:
list.c:169:44: error: comparison with string literal results in unspecified behavior [-Werror=address]
cc1: all warnings being treated as errors
make: ***
[list] Error 1

---

The first one (line 111) is from this:

Code:

---

scanf("&d", &tempProductID);

---

That & should be a %.

The second one, line 169:

Code:

---

if (displayItem -> productName == "")

---

You can't compare strings with ==, you would normally use strcmp. However, if all you're checking is whether a string is empty, you can also check strlen(str) == 0, or if (str[0] == '\0'), which is even more efficient. You also have a very similar error on line 158, though the compiler can't catch it because you are comparing two string variables instead of a string literal.

You have several places that exhibit undefined behavior (which is bad). For starters, everywhere you use the following results in undefined behavior. Read these links for an explanation and alternatives: FAQ > Why fflush(stdin) is wrong - Cprogramming.com and FAQ > Flush the input buffer - Cprogramming.com.

Code:

---

fflush(stdin);

---

Also in your display function, you do this:

Code:

---

checkName[50] = displayItem -> categoryName[50];

---

Both checkName and displayItem->categoryName are arrays of 50 elements, which means that you can only access indexes 0-49 (remember, arrays in C start at 0). So you are writing to memory you don't own which results in undefined behavior. For me, this manifests as your program crashing. For you it may manigest as strange output. That's the thing with undefined behavior, it can be anything at all (even formatting your hard drive, though this is highly unlikely). If you intend to copy whole strings, use strcpy.

You also have similar problems other places, like the following lines in your addItem function:

Code:

---

tempStorage -> categoryName[50] = tempCategoryName[50];
...
tempStorage -> productName[50] = tempProductName[50];

---

Those should also be strcpy(tempStorage->categoryName, tempCategoryName), and similar for product.

That's what I found so far, in a fairly quick read-through of your code. It should be enough to keep you busy for a while.

Thanks! I finally resolved my problem by using strcpy, I feel I'm stupid for making mistake like &d lol.. Thanks for pointing that out :) Learnt a lots of thing, this has been bugging me for whole midnight... again, thanks you!