CODEWITHSUNDEEP
carraysstructmallocrealloc
Jason Per
Jason Per

Reputation: 149

Malloc and Realloc array of structs

I am defining a type of structures

typedef struct structs{
int freeSpace;
} structs;

I am creating a pointer to a structure

structs* arrayOfStructs;

I am allocating memory for array of size 5 of that structure

arrayOfStructs = malloc(5 * sizeof (arrayOfStructs));
arrayOfStructs[3].freeSpace = 99;
printf("\n%d", arrayOfStructs[3].freeSpace);

At some point I am reallocating that memory to array of size 10

arrayOfStructs = realloc(arrayOfStructs, 10 * sizeof (arrayOfStructs));
arrayOfStructs[8].freeSpace = 9;
printf("\n%d", arrayOfStructs[8].freeSpace);

And here I am setting freespace 17 at position 13 of the array which I expect to have only 10 positions.

arrayOfStructs[13].freeSpace = 17;
printf("\n%d", arrayOfStructs[13].freeSpace);
free(arrayOfStructs);

Why is this working ? What am I doing wrong ?

Upvotes: 1

Views: 258

Answers (1)

Bathsheba
Bathsheba

Reputation: 234635

The behaviour of the program is undefined.

You are accessing memory that doesn't belong to you.

(What could well be happening is that realloc is obtaining more memory from the operating system than is actually required).

Upvotes: 5

Related Questions