How to get the length of a dynamically created array of structs in C?

Question

I am currently trying to get the length of a dynamically generated array. It is an array of structs:

typedef struct _my_data_ 
{
  unsigned int id;
  double          


        

Answer 1

mydata* arr = (mydata*) malloc(sizeof(mydata));

is a pointer and not an array. To create an array of two items of mydata, you need to do the following

mydata arr[2];

Secondly, to allocate two elements of mydata using malloc(), you need to do the following:

mydata* arr = (mydata*) malloc(sizeof(mydata) * 2);

OTOH, length for dynamically allocated memory (using malloc()) should be maintained by the programmer (in the variables) - sizeof() won't be able to track it!