printing an array of structs

Question

void print(part *item, int part_count) {
    int i=0;

    for (i=0; i<part_count; i++) {
       printf("Item number: %d\n", i + 1);
       printf("Item name: %s\n", item[i].name);
       printf("Item price: $%f\n", item[i].price);
       printf("Item quantity: %d\n", item[i].quantity);
    }
}

i want to print an array of structs created with a different function. I have looked but have yet to find a different way to print them or what i am doing wrong in the print statements. My program compiles but crashes upon running.

ok well it is good to know the problem is not within these statements. That was frustrating me. here is the add function.

void add(part *item, int *part_count)
 {
      if (!item)
      {
         item = malloc(sizeof(part));
      }

      item = realloc(item, sizeof(part) * *part_count + 1);

      item[*part_count].name = malloc(sizeof(char)*64); // max of 64 characters

      printf("Please enter item name: ");
      scanf("%65s", item[*part_count].name);

      printf("Please enter item price: ");
      scanf("%f", &item[*part_count].price);

      printf("Please enter item quantity: ");
      scanf("%d", &item[*part_count].quantity);

      *part_count = *part_count+ 1;
 }

This portion is correct.. could you post the code that populates the item array? If I had to guess, I'd say item[i].name is not null-terminated... — Robert Martin
– Robert Martin, Commented Mar 7, 2012 at 1:37
Your code fragment looks fine. Please show the code that calls your print, and sets up the array that you print. — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Mar 7, 2012 at 1:38
I would bet that you are calling this with an incorrect part_count parameter. Perhaps a sizeof instead of the number of structures in the array? — Borodin
– Borodin, Commented Mar 7, 2012 at 1:44

Chris Dodd · Accepted Answer · 2012-03-07 18:08:23Z

1

item, being an argument to add is local to that function. So when you modify it, that doesn't affect the variable that you passed in to it. In order to get the modified item pointer back, you need to pass a pointer to it (a pointer to a pointer):

void add(part **item, int *part_count)

Then use *item (or (*item)) everywhere you currently use item within add

edited Mar 7, 2012 at 18:08

answered Mar 7, 2012 at 1:57

Chris Dodd

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Dmitry · Accepted Answer · 2012-03-29 08:21:34Z

void add(part **item, int *part_count)
{
  char temp[100];

  if (!(*item)){
   //printf("first alloc\n");
       *item = malloc(sizeof(part)*3);
  }
  else if (*part_count>= 3){
  //printf("realloc\n");
      *item = realloc(*item, sizeof(part) * (*part_count + 1));
  }

  item[0][*part_count].name = malloc(sizeof(char)*100); // max of 100 characters

  printf("Please enter item name: \n");
  fgets(temp, 100, stdin);     
  strcpy(item[0][*part_count].name, temp);      


  printf("Please enter item price: \n");
  fgets(temp, 100, stdin);
  sscanf(temp, "%f", &item[0][*part_count].price);      


  printf("Please enter item quantity: \n");
  fgets(temp, 100, stdin);
  sscanf(temp, "%d", &item[0][*part_count].quantity);   


  *part_count = *part_count+ 1;
}

This ended up doing it. Not sure if using a **struct was necessary but was the only method I could get working.

Perry · Accepted Answer · 2012-03-07 01:39:04Z

Without seeing the rest of your program, it is impossible to answer this question effectively. However, you mention "crashing on running", which generally means one of:

You are violating the API of some function, passing it incorrectly typed arguments or the wrong number of arguments
You are attempting to dereference or assign through a pointer to non-existent memory.

I would strongly suggest that you try the following things:

First, compile your program (presuming this is gcc) with -Wall -Werror, and pay attention to all the error messages you get and fix all of them.
Second, try examining the stack trace of the core dump you get with gdb -- that will tell you exactly where your program crashed, at least if you compile with -g
Third, try running with a system like Valgrind which is designed to find and diagnose memory errors.

Jonathan Wood · Accepted Answer · 2012-03-07 01:41:24Z

0

The loop appears properly constructed. This suggests the problem lies either with how the data is constructed, or a problem with the arguments that are sent to this function.

answered Mar 7, 2012 at 1:41

Jonathan Wood

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codeomnitrix · Accepted Answer · 2012-03-07 01:42:13Z

0

Youu should write your function as

void print(part item[], int item_count){ ... ... }

And in your function call: print(item, f)

answered Mar 7, 2012 at 1:42

codeomnitrix

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2 Comments

templatetypedef Over a year ago

Why change the * to []? They're equivalent to one another.

Chris Dodd Over a year ago

Indeed, using [] confuses new programmers into thinking that it is an array when its a pointer.

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