Thread: allocating space dynamically for an array of structures

There is no need for the else. If malloc fails, it quits the program and does not continue, so...
And you have never filled in any values for exec_array, so it will print gibberish.
And lastly, of course, you still need that indentation.

Code:

     #include <stdlib.h>
     #include <stdio.h>
     typedef struct exec_time
{
	int execution_time;                
	int process_number;                
	float average_time;            
}exec_time; 

int main()
{
     exec_time *exec_array;
     size_t n;
     printf("Please enter a non-negative integer: ");
     scanf("%d", &n); 
     exec_array = malloc(n *sizeof(*exec_array));
	if(exec_array == NULL)
		{
		printf("\nMemory allocation failed - not enough memory.\n");
		return 1;
		}	
	(*exec_array).execution_time=10;
	(*exec_array).process_number=9;
	(*exec_array).average_time=9.15;
        printf("%d %d %f\n",exec_array->execution_time,exec_array->process_number,exec_array->average_time);
		free(exec_array);
		return 0;	
}

The resulting output of this is 10, 9 and 9.15, - but when i enter an integer from the question "Please enter a non-negative integer: ", am I right in saying this allocates the memory correctly but apart from that does nothing?

perhaps you can try this and see what happens

Code:

exec_array = malloc(n * (sizeof(exec_time)));

Originally Posted by itCbitC

are you sure that this will malloc memory for an object of type exec_time?

No, it will do more than that. It will (assuming that it succeeds) allocate memory for n objects of type exec_time, assuming that *exec_array is of type exec_time. However, it appears that we may have misread the rubric...

Originally Posted by cus

So all I need to know is the program does what its set out to do? Please say yes - or the cat is getting it (only kidding offcourse).

I suppose you are talking about this:

Code:

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

typedef struct exec_time
{
    int execution_time;
    int process_number;
    float average_time;
} exec_time;

int main()
{
    exec_time *exec_array;
    size_t n;

    printf("Please enter a non-negative integer: ");
    scanf("%d", &n);

    exec_array = malloc(n * sizeof(*exec_array));
    if (exec_array == NULL)
    {
        printf("\nMemory allocation failed - not enough memory.\n");
        return 1;
    }
    else
    {
        printf("%d %d %f\n", exec_array->execution_time, exec_array->process_number, exec_array->average_time);
        free(exec_array);
        return 0;
    }
}

Take a look at your problem specification again: "Set up an array of structures and show how to access individual elements of the structures within the array. Then finally, use malloc to allocate space dynamically for a structure of the type structure exec_time."

I originally interpreted that as "use malloc to allocate space dynamically for an array of exec_time structures", but if you posted the problem correctly, then that is wrong. The problem is divided into three parts:

• Define the structure exec_time
• Create an array of structures and access the members of the elements of the array
• Allocate space dynamically for one structure

You have done the first part correctly. The second part does not require dynamic memory allocation using malloc(). You can use a fixed size array. The intention is most probably to test you on how you access the members of the elements of the array. The third part merely requires you to allocate (and presumably deallocate) space for one exec_time structure. You are not required to do anything with the structure (but I suppose you could for bonus marks... unless your teacher is a computer security professional).

Originally Posted by cus

I have tried to indent the code as best i can - I have even looked it up

http://apps.sourceforge.net/mediawik...le=Indentation
Also note how laserlight's code looks compared to yours and look how laserlight has done vs yours.