C程序设计打印链接列表，不沿列表移动并崩溃

Question

I am trying to print a linked list, it is acting strangely, when it is suppose to move to the next item it will not, for instance the first item printed is "Granny Smith" and then the rest in the struct, when it goes to the next line what should be a new food is "ranny Smith" Always without the G, and most of the other details are corrupted or gibberish. Any help would be greatly appreciated.

#define _CRT_SECURE_NO_WARNINGS

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

#define cls system("cls");
#define flush fflush(stdin)
#define pause system("pause");


struct food  // Declaration of struct
{
    char produce[20];
    char type[20];
    char soldBy[20];
    float price;
    int quantityInStock;
    struct food *next;
};


void addPres(struct food** tip, char tokenPro[20], char tokenType[20], char tokenSold[20], float tokenFloat, int tokenInt);
void display ();
void displayMenu ();
int getChoice ();
void readDataIn();




int main()
{
    int choice = 0;
    int ;
    struct food first;
    char *saveFloat, *saveInt;
    char tokenPro[20], tokenType[20], tokenSold[20], savePro[20], saveType[20], saveSold[20], j[1900];
    float tokenFloat, messFloat;
    int danint, tokenInt;
    struct food* a = NULL;
    FILE* file;

    a = NULL; // sets the first item on the list to empty

//readDataIn();
    do
    {
        choice = getChoice();//function to present choices and receive an answer
        switch (choice)//switch routes the choice
        {
        case 1: //to enter a new node on the list
            cls;
            printf("Enter the produce type: ");
            fgets(tokenPro, 20, stdin);
            printf("Enter the type: ");
            fgets(tokenType, 20, stdin);
            printf("Enter the units of measurement: ");
            fgets(tokenSold, 20, stdin);
            printf("\nEnter the price per %s: ", &tokenSold);
            scanf("%f", &tokenFloat );
            printf("\nEnter the quantity in stock: ");
            scanf("%i", &tokenInt );
            //pause;
            addPres(&a, tokenPro, tokenType, tokenSold, tokenFloat, tokenInt);
            break;
        case 2: //to display the linked list
            display(a);

            break;
        case 3: //to reverse the order

            if((file=fopen("AssignmentTwoInput.txt", "r")) != NULL)  //opens files
            {
                while(fgets(j, sizeof(j), file))  //while information is being sent to j from the file
                {
                    strcpy(savePro, strtok(j, ","));
                    strcpy(saveType, strtok(NULL, ","));
                    strcpy(saveSold, strtok(NULL, ","));
                    saveFloat = strtok(NULL, ",");
                    saveInt = strtok(NULL, "\n");
                    messFloat = atof(saveFloat); //ID number is assigned to token2
                    danint = atoi(saveInt); //converts  the value token2 points to into an int (previously read in as an string)
                    addPres(&a, savePro, saveType, saveSold, messFloat, danint); //sends the name and ID to the function to add a person
//printf("\n %s \t %s \t %s \t %f \t %i", savePro, saveType, saveSold, messFloat, danint);
//pause;
                }//end while loop
            }//end if loop
            printf("\nSuccessfully loaded input file\n\n\n"); //message to tell user the back was found and imported successfully
            pause;
            fclose(file);
            break;
        case 4: //to export data

            break;
        case 5: //option to exit

            exit(0);
            break;
        default://error checking
            printf("Please enter a valid choice.\n");
            break;
        }//switch loop close

    }
    while (choice != 5);   //end menu choices


    return 0;
}//end main


void addPres(struct food** tip, char tokenPro[20], char tokenType[20], char tokenSold[20], float tokenFloat, int tokenInt)
{


    struct food* temp =

        (struct food*) malloc(sizeof(struct food));
    strcpy(temp->produce, tokenPro);
    strcpy(temp->type, tokenType);
    strcpy(temp->soldBy, tokenSold);
    temp->price = tokenFloat;
    temp->quantityInStock = tokenInt;

//printf("\n %s \t %s \t %s \t %f \t %i", temp->produce, temp->type, temp->soldBy, temp->price, temp->quantityInStock);
//pause;
    if (tip == NULL) //if the tip node is empty
    {
        tip = temp; //tip node becomes this node
        (*tip)->next = NULL; // since there are no others yet the next node will be empty
    }


    else
    {
        temp->next = tip; // reassigns the tip node to the next one
        (*tip) = temp; //inserts current node as the tip
    }
}

void display(struct food* c)
{
//c = first; //assigns c to the first node on the linked list
    int count = 1;
    struct food *temp;
    temp = c;
    cls;
    printf("==========================================================================\n"); //prints a header to say which info is which
    printf(" Item #   Produce       Type             Sold By         Price    In Stock\n");
    printf("==========================================================================\n");
    while( c != NULL)
    {
        printf("%3i \t", count);
        printf("%s \t", c->produce ); //prints name
        printf("%s \t", c->type ); //prints name
        printf("%s \t", c->soldBy); //prints name
        printf("%-3.2f \t", c->price); //prints ID
        printf("%i\n", c->quantityInStock); //prints ID
        pause;
        count = count + 1;
        c = c->next; //advances to next item in the linked list

        if(c == NULL)
        {
            printf("\n end \n"); //once end is found user is told

            pause;
        }
    }
    printf("\n done \n");
    pause;
}//end display

Answer 1

You have three important mistakes, one of them seems to be caused by copying and pasting some code,

1. This printf() statement would cause undefined behavior

    printf("\\nEnter the price per %s: ", &tokenSold); 

   because you are passing the correct address but the pointer type is wrong so pointer arithmetic will cause undefined behavior inside printf()

    printf("\\nEnter the price per %s: ", tokenSold); /* remove the & --------------------^ here */ 

2. You passed a double pointer to addPres but you never dereference it to access the actual poitner, which is what you want to modify, that is causing both, undefined behavior and the observed effect of an empty list, since once the function returns it did not alter the original poitner, you should access the double pointer with the dereference operator inside this function, for example instead of

    if (tip == NULL) 

   it has to be

    if (*tip == NULL) 

   and the same applies for every access inside this function.

   • How did I find out all these problems so quickly?

     Because I compiled your programs with compiler warnings enabled and it started showing those problems.

   • Will there be other issues in your code?

     Yes probably, but you need to fix these first.

3. You fflush(stdin) , a very common mistake which seems to come from some tutorials or books or online resources, the standard clearly states that fflush() is for output streams, and the behavior is undefined for input streams, the following was taken from the C11 draft

   7.21.5.2 The fflush function

   2. If stream points to an output stream or an update stream in which the most recent operation was not input, the fflush function causes any unwritten data for that stream to be delivered to the host environment to be written to the file; otherwise, the behavior is undefined.