Array with n initialized instance

**Jimmy589** · 04-05-2017

Hello everyone !

I have one more problem with a programming exercise in c.

I have this struct

Code:

struct FluxCapacitor
    {
        unsigned char* c_string;
        unsigned int value;
    };

I initialized the struct and now I want to create an Array which creates n completly initialized instance of my struct.

I started like this

Code:

struct FluxCapacitor** createFluxCapacitorArray(unsigned int n){

    struct Flux **array = malloc(n * sizeof *array); // Flux is the new Struct name

I created a new function and I allocated the memory for the array.

How would my next step look like?

**algorism** · 04-05-2017

If you're just trying to create an array of structs then you don't need a double pointer. Just malloc size elements and then fill them in with a loop, just like with a normal array. Remember to free the array when you're done with it.

**Jimmy589** · 04-05-2017

Well the function name was given in the task position with the double pointer.

I will put my complete code in so its maybe easier to understand what I want to do

Code:

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

struct FluxCapacitor
    {
        unsigned char* c_string;
        unsigned int value;
    };

char* randomString() //Function for random character
{
    unsigned char* character;
    character = malloc(sizeof(unsigned char));
    int i;
    for (i=0; i<3; i++)
    {
        character[i] = (unsigned char) (65+(rand()%26));
    }
    character[3] ='\0';
    return character;
}


void bubbleSortFluxCapacitorArray(struct FluxCapacitor** array, unsigned int n){ //Not in use right now

}

void printFluxCapacitorArray(struct FluxCapacitor** array, unsigned int n){ // Not in use right now



}

struct FluxCapacitor* createFluxCapacitor(){ // Instance of my struct
    struct FluxCapacitor *Flux = malloc( sizeof(*Flux) );
Flux->value = rand();
Flux->c_string = randomString();
};


struct FluxCapacitor** createFluxCapacitorArray(unsigned int n){ //Function for the Array I want to initialize with n instance of the struct

    struct Flux **array = malloc(n * sizeof *array);

    return array;


};

int main()
{


}

**algorism** · 04-05-2017

I don't know what a "task position" is, but if you have your heart set on a double pointer then you could malloc the structs separately. You'll have to free them all separately, too, and then free the pointer array.

Code:

typedef struct FC {
  int x;
} FC;

void *xmalloc(size_t size) {
  void *p = malloc(size);
  if (!p) {
    perror("xmalloc");
    exit(EXIT_FAILURE);
  }
  return p;
}

FC **FC_new(int size) {
  FC **fc = xmalloc(size * sizeof *fc);
  for (int i = 0; i < size; i++) {
    fc[i] = xmalloc(sizeof **fc);
    fc[i]->x = 0;
  }
  return fc;
}

**Jimmy589** · 04-05-2017

I edit my code in and in line 35 I create my instance of the struct. I filled the attributes with random values and now I want to create an Array with n completly initialized instances of my Struct.

For example n would be 10 so I want to fill my Array with 10 instances of the struct. So if I print the Array I would get 10 random numbers from value and 10 random characters.

**algorism** · 04-05-2017

Sounds like a plan. Make it so.

**Jimmy589** · 04-06-2017

Well thats my question how do I do this?

**Salem** · 04-06-2017

> character = malloc(sizeof(unsigned char));
Look at the loop that follows. How many characters do you need to allocate here?

> struct Flux **array = malloc(n * sizeof *array);
I guess you need next is something like
array[i] = createFluxCapacitor();

**Jimmy589** · 04-06-2017

The function looks like this now

The string is 3 characters long so I need to allocate 3*n characters

Code:

struct FluxCapacitor** createFluxCapacitorArray(unsigned int n){ //Function for the Array I want to initialize with n instance of the struct

    struct Flux **array = malloc(n * sizeof *array);

    for (int i = 0 ; i < n ; ++i)
     {
         array[i] = createFluxCapacitor();
     }

};

**Salem** · 04-06-2017

> The string is 3 characters long so I need to allocate 3*n characters
Did you count the \0 at the end?

What does your createFluxCapacitorArray() function return?

**Jimmy589** · 04-06-2017

Yes I count the \0 at the end

It returns the Array

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