CODEWITHSUNDEEP
carraysstruct
Alexis
Alexis

Reputation: 521

How to send the properties of a struct array as a parameter to a function in C?

So here is my problem.

I have a struct that has some properties:

struct foo {
  const uint8_t propertyA;
  int propertyB;
  const int propertyC;
  typeX propertyD;
  typeY propertyE;
};

I then create an array of this struct since I have to represent multiple instances of the object foo:

const int foosQuantity = 8;
struct foo foos[foosQuantity] = 
   {{ .propertyA=0b11001100, .propertyB=0, .propertyC=140, ...},
   { .propertyA=0b11001000, .propertyB=0, .propertyC=150 ...},  

          //*** foosQuantity-3 MORE TIMES ***//

   { .propertyA=0b11001000, .propertyB=0, .propertyC=150 ...}}

Until now everything seems to work. However, I have not figured how to send an array of one type of property to a function. For example, I Have this function written in an extern library that takes an array of propertiesA:

void myFunc(const uint8_t *propertyAs, sizeArray){

    //*** DO STUFF ***//

}

And I would like to send the properties of my struct directly without having to use a for loop that iterates through the struct array and copies the elements.

int main(){

  //*** STUFF ***//

  myFunc(foos.propertyA, foosQuantity); 

  //*** MORE STUFF ***//

  return 0;
}

Is this possible?

Upvotes: 3

Views: 102

Answers (2)

rouzier
rouzier

Reputation: 1180

This is not possible.

You can either

  1. Use a parallel array with just propertyA that gets manipulated along side the array of foo.
  2. Or create an array of propertyA then copy it back in the foo array.

Option 1 is the most memory efficient since it requires the least memory but it may require you to rewrite your a lot of your code.

Option 2 requires the least amount of rework of your code but requires more memory and time.

Upvotes: 1

Govind Parmar
Govind Parmar

Reputation: 21542

If the entire struct array already exists in your program's memory, you aren't going to get more efficient than just passing a pointer to the start of the array, the array's length (in elements), and iterating on the propertyA members of the array:

void bar(struct foo *p, size_t len)
{
    size_t i;
    for(i = 0; i < len; i++)
    {
        dosomething(p[i].propertyA);
    }
}

If you are restricted by assigned specifications to only be allowed to pass an array of propertyA (i.e. uint8_t) to your function, you do have to copy them out of the array of struct foo; there's no way around that.

Upvotes: 5

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