allocating space dynamically for an array of structures

**Elysia** · 01-08-2009

AFAIK, it means that either what you assign to cannot be assigned (ie array), or you are trying to assign something invalid to a variable, or both.

**cus** · 01-08-2009

to clarify what happens in the program - the user is asked to enter how many integers they would like to have for each element - within the structure so that malloc can calculate how much memory to dynamically calculate. The array:

Code:

'time pts[4] = {{4,8,0.75}, {5,10,0.00457}, {27,75,3.4}};'

is only used to test that I could successfully communicate with the structure - I will alter the program so the user can enter values into the array later. For now I would like to discover why I received the error specified when trying to dynamically allocate memory based upon the integers the user inputs. These values are stored in 'qty qty2 and qty3' - and added together in the 'getnumber()' function - This value is then multiplied against 'sizeof', to discover how many bytes to reserve.

Note - I am aware that I am not using this memory allocated correctly at this point

**Elysia** · 01-08-2009

So post up-to-date, indented code so people can locate the line of error.
And better yet, mark the line in question.

**cus** · 01-08-2009

Code:

         #include <stdlib.h>
         #include <stdio.h>
         typedef struct exec_time
    {
        int et;                
        int pn;                
        float at;            
    }time; 

      int qty, qty2, qty3, i;
     int getnumber();
     void printnumber();
     time pts[4] = {{4,8,0.75}, {5,10,0.00457}, {27,75,3.4}}; 

int main()
{
        time *numbers;
        getnumber();
        numbers = malloc( qty * sizeof(int) ); 
        if(numbers != NULL) 
{
               for(i=0; i<qty ; i++) numbers[i] = i+1;      /*THIS IS THE LINE IN QUESTION LINE 22/*
               for(i=0; i<qty ; i++) 
               printf("%d ", numbers[i]);
               printf("\n");
                       free(numbers); /*free allocated memory*/
                       printnumber();
                       return 0;
}
           else {
                    printf("\nMemory allocation failed - not enough memory.\n");
                    return 1;}
}


int getnumber()
{
     printf("\nHow many ints would you like to store for et? ");
     scanf("%d", &qty);
     printf("\nHow many ints would you like to store for pn? ");
      scanf("%d", &qty2);
     printf("\nHow many floats would you like to store for at? ");
     scanf("%d", &qty3);
                qty = qty + qty2 + qty3; /*adds to total number of integers to be used with malloc and sizeof*/
                return qty;
}

void printnumber() /*simply prints the value of the structure*/
{
      printf("\n\nCode et= execution time, pn =process number, at = average time\n");
      printf("Variable 'time' at element 0 et: %d pn: %d at: %f\n",pts[0].et, pts[0].pn, pts[0].at);
      printf("Variable 'time' at element 1 et: %d pn: %d at: %f\n",pts[1].et, pts[1].pn, pts[1].at);
      printf("Variable 'time' at element 2 et: %d pn: %d at: %f at:\n\n",pts[2].et, pts[2].pn, pts[2].at);
}

I have outlined the line in question in a comment above - i cant see how 'numbers', 'i', or 'qty' can be wrong. thanks

**Elysia** · 01-08-2009

What makes you think you can assign an integer to a structure?
And your indentation is all messed up, too.

**cus** · 01-08-2009

Originally Posted by Elysia

What makes you think you can assign an integer to a structure?
And your indentation is all messed up, too.

because i'm a beginner and asking for some help - if i'm doing this the wrong way all i need is some sound advice on how to use malloc to allocate space dynamically for a structure - with the elements stated in the question.

**Elysia** · 01-08-2009

The problem is not about malloc, but you assigning an integer to a non-integer type!

Code:

struct foo {};
int main()
{
    struct foo myfoo;
    myfoo = 10;
}

This is essentially what you are doing. See why it's wrong?

**MikeyIckey** · 01-08-2009

@ line 22 you use array subscripting

Code:

for(i=0; i<qty ; i++) numbers[i] = i+1;

but you never declared 'numbers' to be an array.
could that be the problem?
Just a thought.
Good luck.

**Elysia** · 01-08-2009

No, numbers is a pointer and thus can be used with array notation. However, numbers is a number of structs, not integers, thus it's not a valid assignment.

**cus** · 01-08-2009

yes i can now see that problem - but dont know how to remedy it

**MikeyIckey** · 01-08-2009

Originally Posted by Elysia

No, numbers is a pointer and thus can be used with array notation. However, numbers is a number of structs, not integers, thus it's not a valid assignment.

ooh. ok, i'm still learning that bit myself. Thanks.
or I guess sorry to chime in on something i'm not totally clear on.

**MK27** · 01-08-2009

Originally Posted by cus

yes i can now see that problem - but dont know how to remedy it

You can probably just remove that line. What was it supposed to do? Were you thinking that this would create numbers[0] to numbers[qty]?

**itCbitC** · 01-08-2009

Besides equating a struct to an int value, there is the additional problem of malloc()'ing memory for storing the time struct.

**MK27** · 01-08-2009

Originally Posted by itCbitC

Besides equating a struct to an int value, there is the additional problem of malloc()'ing memory for storing the time struct.

No. That's a typedef definition. There is no struct exec_time time. There is a new variable type, "time", whose prototype was a struct exec_time.

**Elysia** · 01-08-2009

Originally Posted by cus

yes i can now see that problem - but dont know how to remedy it

The question begs what you are trying to do?

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