Thread: Error with a pointer

Several issues with your code:

1) Your assignment of string literals "default" to your char arrays is an incorrect way to do what you are trying to do. Use strcpy().

2) This :

Code:

 if ( choice == 1 ) { }
 else if ( choice == 2 ) {  listRecipes(listPtr); }
 else if ( choice == 3 ) {  listPtr = insertRecipe(listPtr); }
 else if ( choice == 4 ) {  }
 else if ( choice == 5 ) {  }
 else if ( choice == 8 ) {  }
 else if ( choice == 9 ) {  }
 else {  }
}

should be a switch statement for obvious reasons.

3) On a first glance it looks like you are not actually modifying the list when you are inserting elements. If you wish to do so you may want to pass a **struct instead of a *struct (i.e. a pointer containing the address of the address of the head of the list).

The person writing the code you are looking at is obviously also a beginner, so I suggest to stop using that as a reference for anything.

Inside your insert function it looks to me like you are modifying the pointer passed as parameter so in order to do so successfully you need to pass an address to that pointer (i.e. struct element **head)

Then you change what *head points to by assigning *head = my_new_ptr, or whatever the new element pointer you allocate memory for is called ( I think xptr).

What is happening right now in your code is the same as this:

Code:

void my_func(int x){
  x = 3;
}

int main(void){
  int y = 5;
  my_func(y);
  /*THE VALUE OF y is STILL 5 */
  return 0;
}

The same thing is happening to your pointer. You are passing a pointer variable, changing it inside the function, and once you exit the function the pointer still has the old value it had (unallocated garbage).

You need to brush up on pointers a bit. A pointer is essentialy a variable containing an address. In order to change the contents of a variable within a function you need to provide the address of that variable. So in this case, you need to provide the address of a pointer which is of type **. (basically the address of the memory location where the address of the element in the list is located)

He doesn't necessarily need to use a pointer-to-a-pointer. I would suggest doing the same thing in menu that is done in insertRecipe.

If you understand what the first three specific lines (cut out from you code) below do to update 'listPtr' in 'menu', and recognise that the last lines (also cut out from you code) indicate you are not doing the same thing to update 'list' in 'main', then you'll have worked out what you need to do to .

Code:

 else if ( choice == 3 ) {  listPtr = insertRecipe(listPtr); }

struct element *insertRecipe(struct element *listPtr){ //declare funct that needs a element Pointer as argument

    return(listPtr);

Code:

       menu(choice,list);

void menu(int choice, struct element *listPtr){

If that hint doesn't help then I can only conclude that you did not write the code to begin with.

I see two prototypes for menu. One of them that should be deleted is:

Code:

void menu();

"it doesnt run" doesn't tell us much. Always be specific. Is it because it does not compile (you'd show the compile errors if that were the case), or does it produce the wrong output when executed (you'd show the incorrect vs the expected output).

ty

i'm using the program, when i insert recipes all is ok, but when i go to see what it is inserted, i saw only the first recipe, no other inserted, why?

Code:

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

// struct containing recipe
typedef struct {
 char recipeName[40];
 char recipeHowTo[1000];
 int howManyPerson;
 int level;
 int timeToEat;
} recipe;

// struct for list
struct element {
 recipe data;
 struct element *elemPtr;   
};

// prototypes
struct element *menu(int choice, struct element *list);
struct element *insertRecipe(struct element *listPtr);
struct element *editRecipe(struct element *listPtr);
void listRecipes(struct element *listPtr);
void saveRecipes(struct element *listPtr);
struct element *loadRecipes(struct element *listPtr);

int main() {  
  int choice = 2 ;
  struct element *list = NULL;  
  
  int status = 0;
  while( status != 1 ){
     list = loadRecipes(list);   
     list = menu(choice,list);
 }
  
  system("PAUSE");	
  return 0;
}

struct element *menu(int choice, struct element *list){ 
   
    printf("----Recipes for fun\n");
    printf(".1 Search Recipe\n");
    printf(".2 View Recipes\n");
    printf(".3 Insert Recipe\n");
    printf(".4 Edit Recipe\n");
    printf(".5 Delete Recipe\n");
    printf(".8 Set measure system\n");
    printf(".9 Email Recipes\n"); 
    printf("Insert the number corrispondant to what you need and press ENTER!   ");
    scanf("%d",&choice); 
 
 if ( choice == 1 ) { }
 else if ( choice == 2 ) {  listRecipes(list); }
 else if ( choice == 3 ) {  list = insertRecipe(list); }
 else if ( choice == 4 ) {  list = editRecipe(list); }
 else if ( choice == 5 ) {  }
 else if ( choice == 8 ) {  }
 else if ( choice == 9 ) {  saveRecipes(list); }
 else {  }

return(list);
}

// INSERT RECIPE 
struct element *insertRecipe(struct element *listPtr){ //declare funct that needs a element Pointer as argument
    
    //var declairation
    char recipeName[40];  
    char recipeHowTo[1000];
    int howManyPerson = 0;
    int level = 0;
    int timeToEat = 0;
    recipe x; 
    struct element *xPtr; 
    
    //filling info
    printf("Insert the Recipe name:");
    scanf("%s",recipeName);
    strcpy(x.recipeName,recipeName);
    printf("Insert the how to:");
    scanf("%s",recipeHowTo); 
    strcpy(x.recipeHowTo,recipeHowTo);
    printf("Insert for how many person is the recipe ");
    scanf("%d",&howManyPerson);
    x.howManyPerson = howManyPerson; 
    printf("Insert the level of the recipe from 1 to 5 ");
    scanf("%d",&level);
    x.level = level;
    printf("Insert the time needed to prepare the recipe ");
    scanf("%d",&timeToEat);
    x.timeToEat = timeToEat; 
   
    if (listPtr != NULL) { // if list is not empty
        xPtr = (struct element *)malloc(sizeof(struct element)); //allocate mem
        xPtr->data = x; //put x in data of the pointer
        xPtr->elemPtr = listPtr; //put xptr on top list
    }
    else {
        listPtr = (struct element *) malloc(sizeof(struct element));
        listPtr->data = x;
        listPtr->elemPtr = NULL; //listPtr points to end list
        xPtr = listPtr;
    }
    return(listPtr);    
    
}

//EDIT RECIPE
struct element *editRecipe(struct element *listPtr){
    
    struct element *originalValue = listPtr;
    int i = 1;
    int cont = 1;
    int editValue = 0;
    
    if ( listPtr == NULL ) { printf("No recipes in the database\n"); }
    else {
     int i = 1;   
     while ( listPtr != NULL ) {
         printf("%d %s\n",i,listPtr->data.recipeName); i++;
         listPtr = listPtr->elemPtr;  
        }   
    }   
    
    listPtr = originalValue;
    
    printf("Insert the number of the value to edit: ");
    scanf("%d",&editValue);
    
    for(cont=1;cont<i;cont++){
        if (editValue == cont) {            
            printf("Change the Recipe name:");
            scanf("%s",listPtr->data.recipeName);
            printf("Change the how to:");
            scanf("%s",listPtr->data.recipeHowTo); 
            printf("Change for how many person is the recipe ");
            scanf("%d",listPtr->data.howManyPerson);
            printf("Change the level of the recipe from 1 to 5 ");
            scanf("%d",listPtr->data.level);
            printf("Change the time needed to prepare the recipe ");
            scanf("%d",listPtr->data.timeToEat);          
        }
        listPtr = listPtr->elemPtr;
    }
    return(originalValue);
}

//LOAD RECIPES
struct element *loadRecipes(struct element *listPtr){

FILE *filePtr;
recipe x;
struct element *xPtr;

   if(( filePtr = fopen("recipes.txt","rb"))== NULL){
       printf("Error in file opening");
   }
   while( fread(&x,sizeof(recipe),1,filePtr) != NULL ){
       if(listPtr == NULL){
           listPtr = (struct element *) malloc(sizeof (struct element));
           strcpy(listPtr->data.recipeName,x.recipeName);
           strcpy(listPtr->data.recipeHowTo,x.recipeHowTo);
           //strcpy(listPtr->data.howManyPerson,x.howManyPerson);
           //strcpy(listPtr->data.level,x.level);
           //strcpy(listPtr->data.timeToEat,x.t);
           listPtr->elemPtr = NULL;
       }else{
           xPtr = (struct element *) malloc(sizeof (struct element));
           strcpy(xPtr->data.recipeName,x.recipeName);
           strcpy(xPtr->data.recipeHowTo,x.recipeHowTo);
           //strcpy(xPtr->data.howManyPerson,x.howManyPerson);
           //strcpy(xPtr->data.level,x.level);
           //strcpy(xPtr->data.timeToEat,x.t);
           xPtr->elemPtr = xPtr;
           listPtr = xPtr;
       }
       }fclose(filePtr);  
   return(listPtr);
}


//LIST RECIPES
void listRecipes(struct element *listPtr){
    if ( listPtr == NULL ) { printf("No recipes in the database\n"); }
    else {
     while ( listPtr != NULL ) {
         printf("%s\n",listPtr->data.recipeName); 
         listPtr = listPtr->elemPtr;  
        }   
    }   
}

//SAVE TO TXT
void saveRecipes(struct element *listPtr){
    FILE *stream = fopen("recipes.txt","w");
    
    while(listPtr != NULL) {
     fprintf(stream,"%s\n%s\n%d%d%d\n\n",listPtr->data.recipeName,listPtr->data.recipeHowTo,listPtr->data.howManyPerson,listPtr->data.level,listPtr->data.timeToEat);   
     listPtr = listPtr->elemPtr;
    }
    fflush(stream);
    fclose(stream);
}