Significance of array with only one element

Question

I have come across an array with only one element. This array is defined inside a structure. Which goes like this:

typedef struct abc
{
    int variable1;
    char variable2;
    float array[1];
};

I don't understand why this array is required, why can't we define just a variable or define a pointer(considering array property).

I want to use it. How do i use this variable? abc.array[0] seems correct. Isn't it.

Addition I am not using any dynamic memory allocation then what is its significance ?

Possible duplicate of [One element array in struct](https://stackoverflow.com/questions/4559558/one-element-array-in-struct) — Govind Parmar, Jun 08 '17 at 15:42
In C99 better use [flexible array member](https://en.wikipedia.org/wiki/Flexible_array_member). In older standards of C, an array of dimension one was often used. — Basile Starynkevitch, Jun 08 '17 at 15:43
@GovindParmar thank you. Can you please tell me how can i use it. I am not doing any dynamic memory allocation — Vishwajeet Vishu, Jun 08 '17 at 15:46
The answer linked by @GovindParmar contains an example how to call `malloc` for such a struct. — Gerhardh, Jun 08 '17 at 15:52

score 4 · Accepted Answer · answered Jun 08 '17 at 15:51

It's probably what is called the "struct hack". By allocating a large block of memory, the array becomes dynamic. The one element is just a placeholder to make it compile, in fact there will be many floats.

The dynamic array has to be the last element.

Use like this:

struct abc *ptr = malloc(sizeof(struct abc) + (N-1) * sizeof(float));
ptr->variable1 = N; /* usually store length somewhere in struct*/

Significance of array with only one element

1 Answers1