Passing an array of Struct to a sorting function in C

Question

I'm trying to pass an array of struct to a function that works with it and modify its content. I've read many articles but I still cannot find what I need.

I need to pass this array of struct to a function and work with the values of this array, and the modifications need to be global modifications.

Here, I'm actually sorting the values of the areas of this structure; the program gives me this warning and crashes:

warning: passing argument 1 of 'insersort' from incompatible pointer type [-Wincompatible-pointer-types]|

struct rectangle{
    char name[MAXC];
    float x;
    float y;
    float area;
    float perimeter;
};

void insersort(struct rectangle *rect[],int k)
{
    int i,j;
    float x;
    for(i=1;i<k;i++)
    {
        x=rect[i]->area;
        j=i-1;
        while(j>=0 && x<rect[j]->area)
        {
            rect[j+1]->area=rect[j]->area;
            j--;
        }
        rect[j]->area=x;
    }
    return;
}
.....

I call the function like so:

struct rectangle rect[MAX];
insersort(rect,k);

Too much indirection. Define the first function argument either as struct rectangle rect[] or as struct rectangle *rect but not both. Your struct rectangle *rect[] is an array of pointers. — Weather Vane
– Weather Vane, Commented Oct 24, 2020 at 15:26
^^^^^ e.g. in insersort, the parameter should be struct rectangle rect[] and all rect[n]-> should be changed to rect[n]. — WhozCraig
– WhozCraig, Commented Oct 24, 2020 at 15:40

Joshua · Accepted Answer · 2020-10-24 16:04:56Z

1

You wrote

void insersort(struct rectangle *rect[],int k)

and the body of insertof is written as though you meant

void insersort(struct rectangle (*rect)[],int k)

that is, array of pointer to rect

but you probably meant to write it as

void insersort(struct rectangle rect[],int k)

and not use -> inside insertof

answered Oct 24, 2020 at 16:04

Joshua

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3 Comments

Big- D Over a year ago

How is it possible to use for example rect[i].area inside the function, I mean i need to work with pointers since the struct is passed by reference, If I pass the struct as void insersort(struct rectangle rect[],int k) is it passed by reference ? since there is no '*' specified in the parameter of the function, isn't the function working on a copy of it ? tried many and many modifications to the program and none worked. Thanks.

Joshua Over a year ago

@Big-D: Because an array is always passed by reference.

Big- D Over a year ago

Thanks, now it works, I was sure to have to use '->' in function to work with an array struct but i was wrong.

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